Document:

<PAGE>   1
                                                                   EXHIBIT 10.19

                                LOCKUP AGREEMENT

         THIS LOCKUP AGREEMENT (the "AGREEMENT") is entered into as of this __
day of January, by and among ____________________ (the "SHAREHOLDER") and Quanta
Services, Inc., a Delaware corporation (the "COMPANY").

         WHEREAS, the Shareholder holds common stock of the Company or
securities convertible into or exercisable for common stock of the Company
(collectively, "SECURITIES");

         WHEREAS, the Company believes it is in the best interests of its
stockholders to establish an orderly trading market for shares of the Company's
common stock;

         WHEREAS, the Company desires the Shareholder to refrain selling
Securities held by the Shareholder to encourage orderly trading in shares of the
Company's common stock;

         NOW, THEREFORE, in consideration of the premises, and for other good
and valuable consideration, the receipt and sufficiency of which is hereby
acknowledged, the parties hereto agree as follows:

         1. LOCKUP OF SECURITIES. The Shareholder agrees, that without the prior
written consent of the Company, that, until the earlier of the first anniversary
of the date of this Agreement or a Change in Control (as defined in the
Company's 1997 Stock Option Plan), the Shareholder will not make or cause any
sale of any Securities listed on Exhibit I hereto which, as of the date of this
Agreement, the Shareholder owns either of record or beneficially, and which the
Shareholder has the power to control the disposition; provided, however, that
the Shareholder may, without the Company's prior written consent, (i) sell or
otherwise transfer Securities to UtiliCorp United Inc. or any of its
wholly-owned subsidiaries, or (ii) make a gift of Securities without
consideration to an organization exempt from taxation under Section 501(c)(3) of
the Internal Revenue Code of 1986, as amended, or (iii) transfer shares to an
exchange fund if such transfer does not require the Shareholder to file a Form
144 pursuant to the rules of the Securities and Exchange Commission.

         2. CONSIDERATION FOR LOCKUP. In consideration for the Shareholder
agreeing to be bound by the terms of this Agreement, the Company will issue the
Shareholder a non-qualified option to purchase shares of the Company's common
stock under the Company's 1997 Stock Option Plan for one percent (1%) of that
number of shares of common stock equal to the total number of shares of common
stock subject to the terms of this Agreement (or deemed subject to this
Agreement upon conversion or exercise of Securities held by the Shareholder).
The option granted pursuant to this Section 2 shall be exercisable for ten (10)
years from the date of grant, shall have an exercise price equal to the closing
price for the Company's common stock on the date prior to the date of grant,
shall be immediately vested and shall not be cancelable if the

<PAGE>   2

Shareholder ceases to be employed or otherwise provide services to the Company.
The date of grant shall be the date this grant is ratified by a committee of the
Company's board of directors consisting solely of directors who are not
employees of the Company and who will not be offered an agreement substantially
similar to this Agreement contemporaneously with the date of this Agreement.

         3. FAILURE TO ISSUE OPTION. Should the option required by Section 2 of
this Agreement not be issued within 90 days of this Agreement, then this
Agreement shall be null and void and of no further force and effect.

         4. TRANSFER; SUCCESSOR AND ASSIGNS. The terms and conditions of this
Agreement shall inure to the benefit of and be binding upon the respective
successors and assigns of the parties. Nothing in this Agreement, express or
implied, is intended to confer upon any party other than the parties hereto or
their respective successors and assigns any rights, remedies, obligations, or
liabilities under or by reason of this Agreement, except as expressly provided
in this Agreement.

         5. GOVERNING LAW. This Agreement shall be governed by and construed
under the laws of the State of Texas applicable to contracts entered into and
fully to be performed in the State of Texas by residents of the State of Texas.

         6. COUNTERPARTS. This Agreement may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

         7. TITLES AND SUBTITLES. The titles and subtitles used in this
Agreement are used for convenience only and are not to be considered in
construing or interpreting this Agreement.

         8. NOTICES.

                  (a) All notices, requests, demands and other communications
under this Agreement or in connection herewith shall be given or made upon (i)
the Shareholder at such Shareholder's address set forth on the signature page
hereto; and (ii) the Company at Quanta Services, Inc., 1360 Post Oak Boulevard,
Suite 2100, Houston, Texas 77056, attention President and General Counsel.

                  (b) All notices, requests, demands and other communications
given or made in accordance with the provisions of this Agreement shall be in
writing, and shall be sent by overnight courier, or by facsimile with
confirmation of receipt, and shall be deemed to be given or made when receipt is
so confirmed.

                  (c) Any party may, by written notice to the other, alter its
address or respondent, and such notice shall be given in accordance with the
terms of this Section 8.

                                       2
<PAGE>   3

         9. ATTORNEYS' FEES. If any action at law or in equity (including
arbitration) is necessary to enforce or interpret the terms of this Agreement,
the prevailing party shall be entitled to reasonable attorneys' fees, costs and
necessary disbursements in addition to any other relief to which such party may
be entitled as determined by such court, equity or arbitration proceeding.

         10. AMENDMENTS AND WAIVERS. Any term of this Agreement may be amended
with the written consent of the Company and the Shareholder.

         11. SEVERABILITY. If one or more provisions of this Agreement are held
to be unenforceable under applicable law, portions of such provisions, or such
provisions in their entirety, to the extent necessary, shall be severed from
this Agreement and the balance of the Agreement shall be interpreted as if such
provision were so excluded and shall be enforceable in accordance with its
terms.

         12. DELAYS OR OMISSIONS. No delay or omission to exercise any right,
power or remedy accruing to any party to this Agreement, upon any breach or
default of the other party to this Agreement shall impair any such right, power
or remedy of such holder nor shall it be construed to be a waiver of any such
breach or default, or an acquiescence therein, or of or in any similar breach or
default thereafter occurring; nor shall any waiver of any breach or default be
deemed a waiver of any other breach or default theretofore or thereafter
occurring. Any waiver, permit, consent or approval of any kind or character on
the part of any party to this Agreement of any breach or default under this
Agreement, or any waiver on the part of any party of any provisions or
conditions of this Agreement, must be in writing and shall be effective only to
the extent specifically set forth in such writing. All remedies, either under
this Agreement or by law or otherwise afforded to any holder shall be cumulative
and not alternative.

         13. ENTIRE AGREEMENT. This Agreement and the documents referred to
herein constitute the entire agreement between the parties hereto pertaining to
the subject matter hereof, and any and all other written or oral agreements
existing between the parties hereto are expressly canceled.

                                       3

<PAGE>   4

         IN WITNESS WHEREOF, the parties hereto have executed this Agreement as
of the date first above written.

                                                QUANTA SERVICES, INC.

                                                By:
                                                   ---------------------------
                                                   Name:
                                                   Title:

                                           -----------------------------------
                                           Shareholder

                                   Address:
                                                ------------------------------

                                                ------------------------------

                                                ------------------------------

                                       4
<PAGE>   5
                                   EXHIBIT I

                     SECURITIES SUBJECT TO LOCKUP AGREEMENT<PAGE>   1
                         SECOND AMENDMENT AND CONSENT TO
               THIRD AMENDED AND RESTATED SECURED CREDIT AGREEMENT

         THIS SECOND AMENDMENT AND CONSENT TO THIRD AMENDED AND RESTATED SECURED
CREDIT AGREEMENT (this "AMENDMENT") is entered into as of March 21, 2000, among
QUANTA SERVICES, INC., a Delaware corporation ("BORROWER"), the Lenders, as
defined below, and BANK OF AMERICA, N.A., f/k/a NationsBank, N.A., as
administrative agent for the Lenders (in such capacity, the "AGENT").
Capitalized terms used but not defined in this Amendment have the meaning given
such terms in the Credit Agreement (defined below).

                                    RECITALS

         A. The Borrower is party to that certain Third Amended and Restated
Secured Credit Agreement dated as of June 14, 1999 (as amended by the First
Amendment dated as of September 21, 1999, and as may be amended, restated or
supplemented from time to time, the "CREDIT AGREEMENT"), among the Borrower,
Agent, and the lenders from time to time parties thereto (each a "LENDER"
collectively, "LENDERS").

         B. The Borrower proposes to engage in a private offering of senior debt
securities pursuant to the Note Purchase Agreement (defined below).

         C. The Borrower and the Lenders have agreed to amend the Credit
Agreement, to accommodate the issuance of such senior debt securities, subject
to the terms and conditions set out in this Amendment.

         D. The Borrower has requested certain other modifications to the Credit
Agreement and the Lenders are willing to make such modifications, subject to the
terms and conditions set out in this Amendment.

         NOW THEREFORE, in consideration of the premises and other good and
valuable consideration, the receipt and sufficiency of which are acknowledged,
the undersigned agree as follows:

         1. New Definitions. SECTION 1.1 of the Credit Agreement shall be
amended to add the following new definitions:

                  "NOTE PURCHASE AGREEMENT" means that certain Note Purchase
         Agreement dated as of March 1, 2000, among the Borrower, as issuer, and
         the purchasers listed on "Schedule A" attached thereto, as lenders, as
         may be amended, restated or supplemented from time to time.

                  "SENIOR NOTES" means the notes, guarantees, and all other
         obligations now or hereafter arising under or pursuant to the Note
         Purchase Agreement."

         2. Dividends and Negative Pledges. SECTION 6.10(A) of the Credit
Agreement shall be deleted and replaced in its entirety as follows:

                  "(a) The Borrower shall not pay any dividends or other
distributions on its capital stock other than those made wholly in the form of
additional shares of the Borrower's capital stock, provided that, in respect of
any stock split, the Borrower may make cash distributions in lieu of issuing
fractional shares of capital stock which would otherwise result from such stock
split."

         3. Liens. SECTION 6.13 of the Credit Agreement shall be amended to
delete the "and" at the end of clause (k); to delete the period at the end of
clause (l); to add a semicolon and add "and" at the end of clause (l); and to
add a clause (m) so that clauses (k), (l), and (m) read as follows:

<PAGE>   2

                  "(k) Liens created by the Credit Documents;

                   (l) Liens on any assets acquired in an Acquisition, provided
         that all such Liens, other than Permitted Liens listed in (a) through
         (k) of this Section, shall be released and any notice thereof removed
         from the public records on or before thirty (30) days after the date of
         such Acquisition; and

                   (m) Liens created  in connection with the Senior Notes and
         the Note Purchase Agreement."

         4. Indebtedness. SECTION 6.14 of the Credit Agreement shall be amended
to delete the "and" at the end of clause (e); to delete the period at the end of
clause (f); to add a semicolon and "and" at the end of clause (f); and add a
clause (g) so that clauses (e), (f) and (g) read as follows:

                  "(e) Indebtedness incurred in connection with Subordinated
         Debt Investments;

                   (f) other Indebtedness not included within subsections (a)
         through (e) above, provided that such Indebtedness shall not exceed, at
         any one time outstanding, an amount equal to 8.5% of Consolidated Net
         Worth as of the end of the immediately preceding fiscal quarter; and

                   (g) Indebtedness not to exceed $400,000,000 at any time
         under the Senior Notes and the Note Purchase Agreement."

         5. Loans, Advances and Investments. SECTION 6.15 of the Credit
Agreement shall be amended to replace $1,000,000 with $2,500,000 in clause (g);
to delete the "and" at the end of clause (h); to delete the period at the end of
clause (i); to add a semicolon and "and" at the end of clause (i); and add a
clause (j) so that clauses (g), (h), (i) and (j) read as follows:

                  "(g) Investments in Persons other than Borrower or its
         Subsidiaries, provided that all such Investments shall not exceed
         $2,500,000 at any one time;

                   (h) the existing loan to the NorAm Telecommunications, Inc.
         employee stock ownership plan;

                   (i)      as permitted by SECTION 6.11; and

                   (j) Investments in Lightwave L.L.C., an Alabama limited
         liability company (or any of its successors or assigns), provided that
         all Investments (whether by cash or contribution of assets, but
         excluding the reinvestment of its retained earnings) after December 31,
         1999 may not in the aggregate exceed $5,000,000."

         6. Subordinated Debt Investment. SECTION 6.24 of the Credit Agreement
shall be amended to delete each reference to the term "Change of Control" and in
each case replace it with the defined term "Change in Control" so that such
section shall read in its entirety as follows:

                  Section 6.24 Subordinated Debt Investment. The Borrower shall
         provide written notice to the Agent (by confirmed fax to each of the
         Agent and its legal counsel, Porter & Hedges, L.L.P., attention: Mr.
         Nick H. Sorensen (fax no.: 713-226-0277)) of (i) any Change in Control
         within two (2) Business Days following any such Change in Control, and
         (ii) any notice received by the Borrower from any holder of a
         Subordinated Debt Investment exercising any right to require the
         Borrower to redeem all or any part of a Subordinated Debt Investment
         within two (2) Business Days of the

                                        2

<PAGE>   3

         Borrower's receipt thereof. The Borrower shall not redeem all or any
         part of the Indebtedness evidenced by the Enron Subordinated Debt
         Documents as a result of a Change in Control before ten (10) days
         following the date of a Redemption Notice (as defined in the Enron
         Subordinated Debt Documents) or if prohibited by the subordination
         provisions contained therein. The Borrower shall not redeem, pursuant
         to any optional redemption right it may have, all or any part of a
         Subordinated Debt Investment before the Maturity Date. The Borrower
         shall not amend, modify or change in any way any of the Enron
         Subordinated Debt Documents so as to change the stated maturity date of
         the principal of such Indebtedness, or any installment of interest
         thereon, to an earlier date, increase the rate of interest thereon or
         any premium payable on the redemption thereof, change any of the
         redemption or subordination provisions thereof (or the definitions of
         any defined terms contained therein) or otherwise change in any respect
         materially adverse to the interests of the Lenders any of the terms
         thereof, in each case, without the consent of the Majority Lenders.

         7. Events of Default. SECTION 7.1 of the Credit Agreement shall be
deleted and replaced in its entirety as follows (with the underlined portions
showing new or revised language):

         "Section 7.1 Events of Default. Any one or more of the following shall
constitute an Event of Default:

                  (a) default by the Borrower in the payment of the principal
         amount of any Loan or any Reimbursement Obligation when it becomes due
         and payable under this Agreement, or in the payment of any interest
         thereon or any fees payable hereunder within five (5) days following
         the date when due;

                  (b) default by the Borrower in the observance or performance
         of any covenant set forth in SECTIONS 6.6(E), 6.10(A), 6.11, 6.16,
         6.21, or 6.24;

                  (c) default by the Borrower in the observance or performance
         of any provision hereof or of any other Credit Document not mentioned
         in (a) or (b) above which is not remedied within thirty (30) days after
         the earlier of (i) such default or event of default first becoming
         known to any officer of the Borrower, or (ii) notice to the Borrower by
         the Agent of the occurrence of such default or event of default;

                  (d) any representation or warranty made or deemed made herein,
         in any other Credit Document or in any financial or other report or
         document furnished in compliance herewith or therewith by the Borrower
         or any of its Subsidiaries proves untrue in any material respect as of
         the date of the issuance or making, or deemed issuance or making
         thereof;

                  (e) default occurs in the payment when due (after any
         applicable grace period) of Indebtedness in an aggregate principal
         amount of $1,000,000 or more of the Borrower or any of its
         Subsidiaries, or the occurrence of any other default, which with the
         passage of time or notice would permit the holder or beneficiary of
         such Indebtedness, or a trustee therefor, to cause the acceleration of
         the maturity of any such Indebtedness or any mandatory unscheduled
         prepayment, purchase, or other early funding thereof;

                  (f) the Borrower or any of its Subsidiaries (i) has entered
         involuntarily against it an order for relief under the United States
         Bankruptcy Code or a comparable action is taken under any bankruptcy or
         insolvency law of another country or political subdivision of such
         country, (ii) generally does not pay, or admits its inability generally
         to pay, its debts as they become due, (iii) makes a general assignment
         for the benefit of creditors, (iv) applies for, seeks, consents to, or
         acquiesces in, the appointment of a receiver, custodian, trustee,
         examiner, liquidator or similar official for it or any substantial part
         of its property, (v) institutes any proceeding seeking to have entered
         against it an order

                                        3

<PAGE>   4

         for relief under the United States Bankruptcy Code or any comparable
         law, to adjudicate it insolvent, or seeking dissolution, winding up,
         liquidation, reorganization, arrangement, adjustment or composition of
         it or its debts under any law relating to bankruptcy, insolvency or
         reorganization or relief of debtors or fails to file an answer or other
         pleading denying the material allegations of any such proceeding filed
         against it, (vi) makes any board of directors resolution in direct
         furtherance of any matter described in clauses (i)-(v) above, or (vii)
         fails to contest in good faith any appointment or proceeding described
         in SECTION 7.1(G);

                  (g) a custodian, receiver, trustee, examiner, liquidator or
         similar official is appointed for the Borrower or any of its
         Subsidiaries or any substantial part of its property, or a proceeding
         described in SECTION 7.1(F)(V) is instituted against the Borrower or
         any of its Subsidiaries, and such appointment continues undischarged or
         such proceeding continues undismissed or unstayed for a period of sixty
         (60) days;

                  (h) the Borrower or any of its Subsidiaries fails within
         thirty (30) days (or such earlier date as any steps to execute on such
         judgment or order take place) to pay, bond or otherwise discharge, or
         to obtain an indemnity against on terms and conditions satisfactory to
         the Lenders in their reasonable discretion, any one or more judgments
         or orders for the payment of money in excess of $1,000,000 in the
         aggregate which is uninsured or underinsured by at least such amount
         (provided that there is adequate assurance, in the sole discretion of
         the Lenders, that the insurance proceeds attributable thereto shall be
         paid promptly upon the expiration of such time period or resolution of
         such proceeding), which is not stayed on appeal or otherwise being
         appropriately contested in good faith in a manner that stays execution;

                  (i) the Borrower or any of its Subsidiaries fails to pay when
         due an amount aggregating in excess of $1,000,000 that it is liable to
         pay to the PBGC or to a Plan under Title IV of ERISA; or a notice of
         intent to terminate a Plan having Unfunded Vested Liabilities of the
         Borrower or any of its Subsidiaries in excess of $1,000,000 (a
         "MATERIAL PLAN") is filed under Title IV of ERISA; or the PBGC
         institutes proceedings under Title IV of ERISA to terminate or to cause
         a trustee to be appointed to administer any Material Plan; or a
         proceeding is instituted by a fiduciary of any Material Plan against
         the Borrower or any of its Subsidiaries to collect any liability under
         Section 515 or 4219(c)(5) of ERISA and such proceeding is not dismissed
         within thirty (30) days thereafter; or a condition exists by reason of
         which the PBGC would be entitled to obtain a decree adjudicating that
         any Material Plan must be terminated;

                  (j) the Borrower, any Guarantor, any Person acting on behalf
         of the Borrower or any Guarantor, or any governmental, judicial or
         arbitral authority challenges the validity of any Credit Document or
         the Borrower's or any Guarantor's obligations thereunder, or any Credit
         Document ceases to be in full force and effect in all material respects
         or ceases to give to the Agent and the Lenders the rights and powers
         purported to be granted in its favor thereby in all material respects
         other than for any reason solely caused by or within the sole control
         of the Agent or any Lender;

                  (k) a Change in Control shall occur or the common stock of the
         Borrower shall be delisted from the New York Stock Exchange;

                  (l) an Event of Default shall occur and be continuing under
         the Enron Subordinated Debt Documents or any other documents evidencing
         a Subordinated Debt Investment; or --

                  (m) an Event of Default shall occur and be continuing under
         the Note Purchase Agreement, the Senior Notes, or any other document
         evidencing Indebtedness under the Senior Notes or the Note Purchase
         Agreement."

                                        4

<PAGE>   5

         8. Schedules.  SCHEDULE 5.20 to the Credit Agreement is deleted and is
replaced by the SCHEDULE 5.20 attached to this Amendment.

         9. Consent. Each Lender which signs this Amendment consents to the
Agent entering into the following agreements on its behalf: (a) an intercreditor
agreement with the purchasers of the Senior Notes, substantially in the form of
EXHIBIT A attached hereto; (b) an omnibus first amendment to the Pledge
Agreements, substantially in the form of EXHIBIT B; (c) an omnibus first
amendment to the Security Agreements, substantially in the form of EXHIBIT C;
(d) a first amendment to the Patent Collateral Assignment with Quanta Services
of Canada Ltd., substantially in the form of EXHIBIT D; and (e) such other
documents contemplated by the documents listed in clauses (a) through (d) above
as the Agent or its counsel deems reasonable and necessary.

         10. Exhibits. EXHIBIT 4.1B (Form of Pledge Agreement), EXHIBIT 4.1C
(Form of Security Agreement) and EXHIBIT 4.1D (Form of Patent Collateral
Assignment) of the Credit Agreement are hereby amended to reflect the changes
set out in EXHIBIT B, EXHIBIT C, and EXHIBIT D, respectively, as attached to
this Amendment.

         11. Conditions.  This Amendment shall not be effective until each  of
the following have been delivered to the Agent:

                  (a) this Amendment signed by the Borrower, Guarantors, and
         Majority Lenders;

                  (b) an intercreditor agreement substantially in the form of
         EXHIBIT A attached hereto signed by the Agent on behalf of the Lenders
         and the purchasers under the Note Purchase Agreement;

                  (c) a copy of the Note Purchase Agreement duly executed and
         delivered;

                  (d) such other documents as the Agent may reasonably request.

         12. Fees and Expenses.  The Borrower agrees to pay the reasonable fees
and expenses of counsel to Agent for services rendered in connection with the
preparation, negotiation and execution of this Amendment.

         13. Representations and Warranties. The Borrower and Guarantors
represent and warrant to the Lenders that they possess all requisite power and
authority to execute, deliver and comply with the terms of this Amendment, which
has been duly authorized and approved by all requisite corporate action on the
part of the Borrower and Guarantors, for which no consent of any Person is
required, and which will not violate their respective organizational documents,
and agree to furnish the Lenders with evidence of such authorization and
approval upon request. The Borrower and Guarantors further represent and warrant
to the Lenders that (a) the representations and warranties in each Credit
Document to which they are a party are true and correct in all material respects
on and as of the date of this Amendment as though made on the date of this
Amendment (except to the extent that (i) such representations and warranties
speak to a specific date or (ii) the facts on which such representations and
warranties are based have been changed by transactions contemplated by the
Credit Agreement), (b) it is in full compliance with all covenants and
agreements contained in each Credit Document to which it is a party, and (c) no
Default or Event of Default has occurred and is continuing.

         14. Scope of Amendment; Reaffirmation; Release. Except as affected by
this Amendment, the Credit Documents are unchanged and continue in full force
and effect. However, in the event of any inconsistency between the terms of the
Credit Agreement as hereby amended and any other Credit Document, the terms of
the Credit Agreement shall control and such other document shall be deemed to be
amended

                                        5

<PAGE>   6

hereby to conform to the terms of the Credit Agreement. All references to the
Credit Agreement shall refer to the Credit Agreement as amended by this
Amendment. The Borrower and Guarantors hereby reaffirm their respective
obligations under, and agree that, all Credit Documents to which they are a
party remain in full force and effect and continue to evidence their respective
legal, valid and binding obligations enforceable in accordance with their terms
(as the same are affected by this Amendment). The Borrower and Guarantors hereby
release the Lenders from any liability for actions or failures to act in
connection with the Credit Documents prior to the date hereof. This Amendment
shall be binding upon and inure to the benefit of each of the undersigned and
their respective successors and permitted assigns.

         15. Miscellaneous.

                  (a) No Waiver of Defaults. This Amendment does not constitute
         a waiver of, or a consent to, any present or future violation of or
         default under, any provision of the Credit Documents, or a waiver of
         the Lenders' right to insist upon future compliance with each term,
         covenant, condition and provision of the Credit Documents, and the
         Credit Documents shall continue to be binding upon, and inure to the
         benefit of, the Borrower, Guarantors, and the Lenders and their
         respective successors and assigns.

                  (b) Form. Each agreement, document, instrument or other
         writing to be furnished Agent under any provision of this instrument
         must be in form and substance satisfactory to Agent and its counsel.

                  (c) Multiple Counterparts. This Amendment may be executed in
         any number of counterparts with the same effect as if all signatories
         have signed the same document. All counterparts must be construed
         together to constitute one and the same instrument.

                  (d) Governing Law. This Amendment and the other Credit
         Documents must be construed-and their performance enforced-under Texas
         law.

         16. Entirety. THE CREDIT DOCUMENTS REPRESENT THE FINAL AGREEMENT
BETWEEN THE BORROWER, GUARANTORS AND THE LENDERS AND MAY NOT BE CONTRADICTED BY
EVIDENCE OF PRIOR, CONTEMPORANEOUS, OR SUBSEQUENT ORAL AGREEMENTS BY THE
PARTIES. THERE ARE NO UNWRITTEN ORAL AGREEMENTS AMONG THE PARTIES.

         The Amendment is executed as of the date set out in the preamble to
this Amendment.

                                  QUANTA SERVICES, INC.

                                  By:
                                     -------------------------------------------
                                       James H. Haddox
                                       Chief Financial Officer

                                  BANK OF AMERICA, N.A., as Administrative Agent
                                  and as a Lender

                                  By:
                                     -------------------------------------------
                                       Craig S. Wall
                                       Senior Vice President

                                  6
<PAGE>   7

                                  BANK ONE, TEXAS, NATIONAL ASSOCIATION,
                                  as a Documentation Agent and as a Lender

                                  By:
                                     -------------------------------------------
                                       Name:
                                       Title:

                                  BANKBOSTON, N.A., as a Documentation Agent
                                  and as Lender

                                  By:
                                     -------------------------------------------
                                       Name:
                                       Title:

                                  CREDIT LYONNAIS NEW YORK BRANCH, as a
                                  Managing Agent and as a Lender

                                  By:
                                     -------------------------------------------
                                       Name:
                                       Title:

                                  THE BANK OF NOVA SCOTIA, as a Managing Agent
                                   and as a Lender

                                  By:
                                     -------------------------------------------
                                       Name:
                                       Title:

                                  NATIONAL CITY BANK, as a Lender

                                  By:
                                     -------------------------------------------
                                       Michael J. Durbin
                                       Vice President

                                       7
<PAGE>   8

                                  LASALLE BANK NATIONAL ASSOCIATION, as a
                                  Lender

                                  By:
                                     -------------------------------------------
                                       Richard J. Kress
                                       Vice President

                                  FIRST UNION NATIONAL BANK, as a Lender

                                  By:
                                     -------------------------------------------
                                       Name:
                                       Title:

                                  COMERICA BANK, as a Lender

                                  By:
                                     -------------------------------------------
                                       Mark B. Grover
                                       Vice President

                                  THE BANK OF TOKYO-MITSUBISHI, LTD., as a
                                  Lender

                                  By:
                                     -------------------------------------------
                                       Name:
                                       Title:

                                  CHASE BANK OF TEXAS, N.A., as a Lender

                                  By:
                                     -------------------------------------------
                                       Name:
                                       Title:

                                  GUARANTY FEDERAL BANK, F.S.B., as a Lender

                                  By:
                                     -------------------------------------------
                                       Kevin J. Hanigan
                                       Senior Vice President

                                       8

<PAGE>   9

                                  SUNTRUST BANK, ATLANTA, as a Lender

                                  By:
                                     -------------------------------------------
                                       David Edge
                                       Vice President

                                  By:
                                     -------------------------------------------
                                       Name:
                                       Title:

                                  BANKERS TRUST COMPANY, as a Lender

                                  By:
                                     -------------------------------------------
                                       Name:
                                       Title:

Exhibit A - Form of Intercreditor Agreement
Exhibit B - Form of Omnibus Amendment
Exhibit C - Form of Omnibus Amendment
Exhibit D - Form of First Amendment

                                        9

<PAGE>   10

                        GUARANTORS' CONSENT AND AGREEMENT

         As an inducement to the Lenders to execute, and in consideration of the
Lenders' execution of this Amendment, each of the undersigned hereby consents to
this Amendment and agrees that the same shall in no way release, diminish,
impair, reduce or otherwise adversely affect the obligations and liabilities of
the undersigned under their respective Guaranties described in the Credit
Agreement executed by the undersigned, or any agreements, documents or
instruments executed by any of the undersigned, all of which obligations and
liabilities are, and shall continue to be, in full force and effect. This
consent and agreement shall be binding upon the undersigned, and their
respective successors and assigns, and shall inure to the benefit of the
Lenders, and their respective successors and assigns.

                             Advanced Communication Technologies, Inc.
                             Arby Construction, Inc.
                             Austin Trencher, Inc.
                             CCLC, Inc.
                             Computapole, Inc.
                             Conti Communications, Inc.
                             Crown Fiber Communications, Inc.
                             Dillard Smith Construction Company
                             Driftwood Electrical Contractors, Inc.
                             Edwards Pipeline Company,  Inc.
                             Environmental Professional Associates, Limited
                             Fiber Technology, Inc.
                             Five Points Construction Company
                             GEM Engineering Co., Inc.
                             Golden State Utility Co.
                             Grand Electric Company
                             H.L. Chapman Pipeline Construction, Inc.
                             Haines Construction Company
                             Harker & Harker, Inc.
                             Intermountain Electric, Inc.
                             Manuel Bros., Inc.
                             Network Communications Services, Inc.
                             NorAm Telecommunications, Inc.
                             North Pacific Construction Company
                             North Sky Communications
                             Northern Line Layers, Inc.
                             Pac West Construction, Inc.
                             PAR Electrical Contractors, Inc.
                             PDG Electric Company
                             Potelco, Inc.
                             QSI, Inc.
                             Quanta Acquisition XLV, Inc.
                             Quanta Delaware, Inc.
                             Quanta L Acquisition, Inc.
                             Quanta LI Acquisition, Inc.
                             Quanta LII Acquisition, Inc.
                             Quanta LIII Acquisition, Inc.
                             Quanta Services Management Partnership, L.P.
                             Quanta Utility Installation Co., Inc.
                             Quanta XLI Acquisition, Inc.
                             Quanta XLII Acquisition, Inc.
                             Quanta XLIII Acquisition, Inc.

                                       10

<PAGE>   11

                             Quanta XLIV Acquisition, Inc.
                             Quanta XLIX Acquisition, Inc.
                             Quanta XLVI Acquisition, Inc.
                             Quanta XLVII Acquisition, Inc.
                             Quanta XLVIII Acquisition, Inc.
                             Quanta XVII Acquisition, Inc.
                             Quanta XXXIX Acquisition, Inc.
                             R. A. Waffensmith & Co., Inc.
                             Ranger Directional, Inc.
                             S.K.S. Pipeliners, Inc.
                             Seaward Corporation
                             Spalj Construction Company
                             Specialty Drilling, Inc.
                             Sullivan Welding, Inc.
                             Sumter Builders, Inc.
                             Telecom Network Specialists, Inc.
                             The Ryan Company, Inc.
                             Tom Allen Construction Company
                             TRANS TECH Electric, Inc.
                             Trawick Construction Co.
                             TTM, Inc.
                             TVS Systems, Inc.
                             Underground Construction Co., Inc.
                             Utilco, Inc.
                             VCI Telecom, Inc.
                             W.H.O.M. Corporation
                             Wade D. Taylor, Inc.
                             West Coast Communications, Inc.
                             World Fiber, Inc.

                             By:
                                ------------------------------------------------
                                  Brad Eastman, President or Vice President of
                                  each Guarantor

                             Coast To Coast, LLC

                             By:  Environmental Professional Associates,
                                  Limited, Its Member

                                  By:
                                     -------------------------------------------
                                       Brad Eastman, Vice President

                             By:  Quanta Services, Inc., Its Member

                                  By:
                                     -------------------------------------------
                                       Brad Eastman, Vice President

                             Quanta Services Management Partnership, L.P.

                             By:  QSI, Inc., Its General Partner

                                  By:
                                     -------------------------------------------
                                       Brad Eastman, Vice President

                                       11

<PAGE>   12

                                  SCHEDULE 5.20

                     LIST OF EXISTING LIENS AND INDEBTEDNESS
                            (REVISED MARCH 21, 2000)

1.   Liens listed on SCHEDULE 6.13.

2.   Liens listed on Annex 1 to this SCHEDULE 5.20 which are to be released by
     no later than April 30, 2000.

3.   The following Indebtedness:

<TABLE>
<CAPTION>
           Company                             Amount                 Creditor
           -------                             ------                 --------
<S>                                           <C>               <C>
PAR Electrical Contractors                    286,729           Caterpillar
Potelco                                       367,556           First National Auto Leasing
Trans Tech                                    270,247           Norwest Equipment Financing
                                               79,405           National City Leasing
Union Power                                   183,155           Ford Motor Credit
Golden State Utility                          172,673           Safeco Credit
                                               45,971           GMAC
                                               13,426           Case Credit
                                               32,808           Ford Motor Credit
NorAm Telecommunications                      138,069           GMAC
                                              121,750           Case Credit
Environmental Professional Associates          88,203           Ford Motor Credit
Underground Construction                      130,553           Caterpillar
                                              795,758           GE Capital
Sumter Builders                               494,727           USL Fleet Services
Manuel Brothers                                49,024           Al Manuel
                                              142,248           KDC Financial
Dillard Smith Construction                     32,457           US Bancorp
                                              378,364           William Dillard Smith
                                              316,332           Caterpillar
PDG                                           136,933           CIT Group
Tom Allen Construction                        678,076           Bank One Leasing
Chapman                                        18,625           Ford Motor Credit
                                              463,822           KDC Financial
                                            4,387,386           Safeco
                                            3,782,266           Financial Federal Credit
                                          -----------
Total Indebtedness                         13,606,563
</TABLE>

<PAGE>   13

                                                      ANNEX 1 TO SCHEDULE 5.20

<TABLE>
<CAPTION>
                 DEBTOR                                                                       Filing           Filing
              NAME/ADDRESS                 Secured Party                  Jurisdiction       Number            Date      Collateral
              ------------                 -------------                  ------------       ------           -------    ----------
<S>                                 <C>                                   <C>              <C>                <C>         <C>
Advanced Communication              AT&T Commercial Finance Corp.         Oregon           42602 UCC-1        10/11/96    blanket
Technologies, Inc.                  assigned to                                            42597 assignment
                                    Finova Capital Corporation

Advanced Communication              Finova Capital Corporation            Oregon           51646 UCC-1        7/17/98     blanket
Technologies, Inc.

Manuel Bros., Inc.                  US Bancorp Leasing & Financial        California       431361025 UCC-1    10/19/94    equipment
                                                                                           9162C0360 cont      6/7/99
                                                                                           817560341 UCC-1    6/22/98

Noram Telecommunications, Inc.      Case Credit Corporation               Oregon           35434 UCC-1        8/20/96     equipment
                                                                                           43809 UCC-1        10/22/96
                                                                                           78296 UCC-1        6/19/97
                                                                                           39481 UCC-1        9/19/96

Noram Telecommunications, Inc.      Western Power & Equipment             Oregon           78296               6/9/97     equipment

Noram Telecommunications, Inc.      AT&T Commercial Finance Corporation   Oregon           42597 UCC-1        10/11/96    blanket
15701 S.E. 135th Avenue             assigned to                                            42597 assignment    4/8/98
Clackamas, OR 97105
                                    Finova Capital Corporation
                                    1060 First Avenue
                                    King of Prussia, PA 19406

Northern Line Layers                Modern Machinery                      Montana          55798               4/4/95     equipment

Northern Line Layers                Roland Machinery Company              Montana          59087               4/6/99     equipment

TTM, Inc. f/k/a                     Branch Banking and Trust Co.          North Carolina   000894522 UCC-1     6/1/92     blanket
C&P Enterprises of Charlotte, Inc.  f/k/a Southern National Bank of N.C.                   001447392 cont      4/7/97
d/b/a The Telephone Man                                                                    01549196 amend      3/9/98
1000 Atando Ave
Charlotte, NC 28206
Union Power Construction Company    Associates Leasing, Inc.              Colorado         9982061271         9/28/98     equipment
                                                                                           9972118402         12/19/97
                                                                                           9992012289          3/4/99

Union Power Construction Company    U.S. Bancorp Leasing and Financial    Colorado         52058020           12/12/95    equipment

Valverde Communications, Inc.       Sanwa Bank California                 California       706460970 UCC-1    2/27/97     blanket
</TABLE>

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