Document:

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                                                                    EXHIBIT 10.2

                           [PLEXUS CORP. LETTERHEAD]
                                     WAIVER

September 15, 2000

Firstar Bank,
National Association
777 East Wisconsin Avenue
Milwaukee, Wisconsin 53202

Harris Trust and Savings Bank
111 West Monroe Street
Chicago, Illinois 60603

Bank One, NA
111 East Wisconsin Avenue
P.O. Box 2033
Milwaukee, Wisconsin 53201

Ladies and Gentlemen:

         Please refer to that certain Amended and Restated Credit Agreement
dated as of June 15, 2000, as amended (the "Credit Agreement") between the
undersigned Plexus Corp., a Wisconsin corporation (the "Company") and each of
you (collectively, the "Banks" and individually a "Bank").  All capitalized
terms used and not otherwise defined herein shall have the meanings given to
such terms by the Credit Agreement.

         1.       Background.  The Company has notified the Agent and the Banks
that it wishes to borrow up to $60,000,000 from Bank One, NA on a short-term
basis pursuant to a Demand Note in substantially the form attached hereto as
Exhibit 1 (the "Demand Note").  The Company's obligations on the Demand Note
would be guaranteed by the Guarantors pursuant to their respective Guaranties.
Such borrowing and guaranties would be in conflict with sections 5.1 and 5.8 of
the Credit Agreement, and the Company has requested that the Banks waive such
covenant violations.  Subject to all of the terms and conditions hereof, the
Banks are willing to grant such waiver as set forth below.

         2.       Waiver.  Effective as of the date hereof, the Banks hereby
consent to the borrowing by the Company of up to $60,000,000 pursuant to the
terms of the Demand Note attached hereto as Exhibit 1 and the guaranty of the
Company's obligations under the Demand
<PAGE>   2
Note pursuant to the Guaranties, and waive the violations that would otherwise
occur under sections 5.1 and 5.8 of the Credit Agreement as a result of such
borrowing and guaranty.

         3.       Conditions. Notwithstanding the foregoing, this Waiver shall
not become effective unless and until it has been approved in writing by all
parties to the Credit Agreement.

         4.       Representations and Warranties.  The Company repeats and
reaffirms the representations and warranties set forth in Article IV of the
Credit Agreement.

         5.       Confirmation of Agreements.  Except as expressly provided
above, the Credit Agreement and the Guaranties shall remain in full force and
effect, and this Waiver shall not release, discharge or satisfy any present or
future debts, obligations or liabilities to the Banks of the Company, any
Guarantor or other person or entity liable for payment or performance of any
such debts, obligations or liabilities of the Company, or waive any default.

         6.       Miscellaneous.  The Company shall be responsible for the
payment of all fees and out-of-pocket disbursements incurred by the Agent in
connection with the preparation, execution, delivery, administration and
enforcement of this Waiver and including without limitation the reasonable fees
and disbursements of counsel for the Agent, whether or not any transaction
contemplated by this Waiver is consummated.  The provisions of this Waiver
shall inure to the benefit of and be binding upon any successor to any of the
parties hereto.  All agreements, representations and warranties made herein
shall survive the execution of this Waiver and the making of the loans under
the Credit Agreement.  This Waiver shall be governed by and construed in
accordance with the laws of the State of Wisconsin without regard to its
conflicts of law principles.  This Waiver may be signed in any number of
counterparts with the same effect as if the signatures hereto were upon the
same instrument.

         If the foregoing is satisfactory to you, please sign the form of
acceptance below and return a signed counterpart hereof to the Company.

                                             Very truly yours,

                                             PLEXUS CORP.

(Corporate Seal)

                                             By: /s/ Lisa M. Kelley
                                                -----------------------
                                                Title: Treasurer
                                                      -----------------

                                       2
<PAGE>   3

         Agreed to as of the date first above written.

                                         FIRSTAR BANK,
                                          NATIONAL ASSOCIATION

                                         By:  /s/
                                            -----------------------
                                             Title: Vice President
                                                   ----------------

                                         HARRIS TRUST AND SAVINGS BANK

                                         By: /s/
                                            -----------------------
                                            Title: Vice President
                                                   ----------------

                                         BANK ONE, NA (MAIN OFFICE CHICAGO)

                                         By: /s/
                                            ------------------------
                                            Title: Managing Director
                                                   -----------------

                                      -3-
<PAGE>   4
                                                                    EXHIBIT 10.2

                                  DEMAND NOTE

$60,000,000                                                 September 15, 2000

          FOR VALUE RECEIVED, Plexus Corp., a Wisconsin corporation, promises
to pay to the order of Bank One, NA (the "Bank"), the principal sum of Sixty
Million Dollars ($60,000,000), on November 30, 2000 (the "Maturity Date") or
upon earlier demand by the Bank.

          1.  INTEREST.  This Note shall bear interest at a per annum rate
equal to the Prime Rate announced by the Bank from time to time, changing as
and when such Prime Rate changes, payable with principal on the Maturity Date
or upon earlier demand by the Bank.

          2.  CALCULATION OF INTEREST.  Interest will be computed for the
actual number of days principal is unpaid, using a daily factor obtained by
dividing the stated interest rate by 360.

          3.  INCREASED INTEREST RATE.  Principal amounts remaining unpaid
after the Maturity Date or after demand for payment has been made or the
occurrence of automatic acceleration hereunder shall bear interest from and
after that date in time until paid at a rate of 2% per annum plus the rate
otherwise payable hereunder.

          4.  PREPAYMENT.  This Note may be prepaid in full or in part at any
time without premium or penalty.

          5.  CREDIT BALANCES; SETOFF.  As additional security for the payment
of the obligations described in this Note (collectively the "Obligations"), the
Borrower hereby grants to the Bank a security interest in, a lien on and an
express contractual right to set off against all depository account balances,
cash and any other property of the Borrower now or hereafter in the possession
of the Bank. The Bank may, at any time after demand for payment has been made
or upon the occurrence of automatic acceleration hereunder set off against the
Obligations without any advance or contemporaneous notice or demand of any kind
to the Borrower, such notice and demand being expressly waived.

          6.  PAYMENTS.  Payments due under this Note shall be made in lawful
money of the United States, and the Bank is authorized to charge payments due
against any account of the Borrower. All payments may be applied by the Bank to
principal, interest and other amounts due in any order which the Bank elects.

          7.  PAYMENT DUE ON DEMAND; AUTOMATIC ACCELERATION.  All amounts
outstanding under this Note are due ON DEMAND. Notwithstanding the foregoing,
the unpaid principal balance of this Note, together with all interest accrued
thereon, shall automatically become immediately due and payable, without
presentment, demand, protest or further notice of any kind, all of which are
hereby waived, if any bankruptcy, insolvency or receivership proceedings, or an
assignment for the benefit of creditors shall be commenced under any Federal or
state law by or against the Borrower.

<PAGE>   5
     8.   ADDITIONAL BANK RIGHTS.  Without affecting the liability of any
Borrower, endorser, surety or guarantor, the Bank may, without notice, renew or
extend the time for payment, accept partial payments, release or impair any
collateral security for the payment of this Note, or agree not to sue any party
liable on it.

     9.   WARRANTIES. The Borrower makes the following warranties: (A) It is a
validly existing corporation, in good standing under the laws of its state of
organization, and has all requisite power and authority, corporate or otherwise,
and possesses all licenses necessary, to conduct its business and own its
properties. (B) The execution, delivery and performance of this Note (i) are
within the Borrower's power; (ii) have been duly authorized by proper corporate
action; (iii) do not require the approval of any governmental agency; and (iv)
will not violate any law, agreement or restriction by which the Borrower is
bound.  (C) This Note is the legal, valid and binding obligation of the
Borrower, enforceable against the Borrower in accordance with its terms.

     10.  WAIVERS; RELATIONSHIP TO OTHER DOCUMENTS. The Borrower and all
endorsers, sureties and guarantors waive presentment, protest, demand, and
notice of dishonor.  The warranties, covenants and other obligations of the
Borrower (and rights and remedies of the Bank) in this Note and all related
documents are intended to be cumulative and to supplement each other.

     11.  EXPENSES AND ATTORNEYS' FEES. The Borrower will reimburse the Bank and
any participant in the Obligations ("Participant") for all reasonable attorneys'
fees and all other reasonable costs, fees and out-of-pocket disbursements
(including fees and disbursements of both inside counsel and outside counsel)
incurred by the Bank or any Participant in connection with the preparation,
execution, delivery, administration, defense and enforcement of this Note,
including fees and costs related to any waivers or amendments with respect
thereto.  The Borrower will also reimburse the Bank and any Participant for all
costs of collection before and after judgment, and the reasonable costs of
preservation and/or liquidation of any collateral (including fees and
disbursements of both inside and outside counsel).

     12.  APPLICABLE LAW AND JURISDICTION; INTERPRETATION; JOINT LIABILITY. This
Note shall be governed by and interpreted in accordance with the laws of the
state of Wisconsin without regard to its conflicts of law principles, except to
the extent superseded by Federal law.  Invalidity of any provisions of this Note
shall not affect any other provision. THE BORROWER HEREBY CONSENTS TO THE
EXCLUSIVE JURISDICTION OF ANY STATE OR FEDERAL COURT SITUATED IN THE COUNTY OR
FEDERAL JURISDICTION OF THE BANK'S MILWAUKEE OFFICE, AND WAIVES ANY OBJECTION
BASED ON FORUM NON CONVENIENS, WITH REGARD TO ANY ACTIONS, CLAIMS, DISPUTES OR
PROCEEDINGS RELATING TO THIS NOTE, THE COLLATERAL, ANY OTHER LOAN DOCUMENT, OR
ANY TRANSACTIONS ARISING THEREFROM, OR ENFORCEMENT AND/OR INTERPRETATION OF ANY
OF THE FOREGOING. Nothing herein shall affect the Bank's rights to serve process
in any manner permitted by law, or limit the Bank's right to bring proceedings
against the Borrower in the

                                      -2-
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competent courts of any other jurisdiction or jurisdictions.  This Note, and
any amendments hereto (regardless of when executed) will be deemed effective
and accepted only upon the Bank's receipt of the executed originals thereof.

         13.   WAIVER OF JURY TRIAL.  THE BORROWER AND THE BANK HEREBY
JOINTLY AND SEVERALLY WAIVE ANY AND ALL RIGHT TO TRIAL BY JURY IN ANY ACTION OR
PROCEEDING RELATING TO ANY OF THE LOAN DOCUMENTS, THE OBLIGATIONS THEREUNDER,
ANY COLLATERAL SECURING THE OBLIGATIONS, OR ANY TRANSACTION ARISING THEREFROM
OR CONNECTED THERETO.  THE BORROWER AND THE BANK EACH REPRESENTS TO THE OTHER
THAT THIS WAIVER IS KNOWINGLY, WILLINGLY AND VOLUNTARILY GIVEN.

                                Plexus Corp.

                                By: /s/ Lisa M. Kelley
                                    ------------------

                                    Name and Title: Lisa M. Kelley
                                                    --------------------------
                                                    VP - Finance & Treasurer

                                      -3-<PAGE>   1

                                                                     EXHIBIT 4.3

                       MISSISSIPPI VALLEY BANCSHARES, INC.
                   1991 STOCK OPTION PLAN (FIVE-YEAR OPTIONS)
                          (As Amended Through 4/19/00)

         1. Purpose of Plan: The purpose of this 1991 Stock Option Plan
(Five-Year Options) (the "Plan") is to aid Mississippi Valley Bancshares, Inc.
(the "Company") and its subsidiaries in securing and retaining officers by
making it possible to offer them an increased incentive, in the form of a
proprietary interest in the Company, to join or continue in the service of the
Company (including its subsidiaries) and increase their efforts for its welfare.

         2. Granting of Options: The Compensation and Employee Benefits
Committee ("Committee") of the Company's Board of Directors ("Board") may from
time to time grant options to purchase shares of the Company's common stock
("Stock") to officers of the Company or any of its subsidiaries pursuant to this
Plan. In granting options, the Committee may consider the recommendations of the
Company's Chairman and the chief executive officers of the Company's
subsidiaries. No member of the Committee shall be eligible to participate in the
decision to grant options under this Plan if such member has been granted or
awarded equity securities of the Company under this Plan or any other plan of
the Company during the one year before the commencement of such member's service
on the Committee or during such service.

         The total number of Shares that may be optioned under the Plan from
time to time is 1,640,000 less the number of shares subject to outstanding or
exercised options under the Company's 1988 Stock Option Plan (Five-Year
Options). Shares optioned may consist, in whole or in part, of unissued Shares
or reacquired Shares. If any Shares that have been optioned cease to be subject
to option, they may again be optioned under the Plan and for the purpose of this
Section 2 shall not be considered as having been theretofore optioned. The
foregoing number of Shares may be increased or decreased by events stated in
Section 4.

         No option may be granted under the Plan before the date on which this
Plan is adopted by the Board or after December 31, 2009, unless this Plan is
extended, but options theretofore granted may extend beyond that date. No option
holder ("Participant") shall have any rights of a stockholder as to Shares under
option until such Shares shall have been issued to the Participant upon due
exercise of the option.

         3. Terms of Options: The terms of each option granted under the Plan
shall be as determined from time to time by the Committee, consistent however,
with the following:

         (a)      The option price shall be not less than the last sale price of
                  the Stock as reported on the NASDAQ National Market System on
                  the date the option is granted. Payment in full in cash shall
                  be made for all Shares purchased.

         (b)      No option shall be exercisable after five years from the date
                  it is granted, except as provided in subparagraph (e).

         (c)      Each option shall be for a maximum of 15,000 Shares and shall
                  not vest earlier than at the rate of 25% of the total number
                  of Shares subject to the

                                      -1-

<PAGE>   2

                  option for each full year elapsed since the date the option is
                  granted, subject to acceleration in the event of a change in
                  control of the Company.

         (d)      The option shall not be transferable by the Participant
                  otherwise than by will or by laws of descent and distribution,
                  and except as provided in subparagraph (e) the option shall be
                  exercisable only by the Participant and only during the period
                  of the Participant's employment by the Company or any of its
                  subsidiaries.

         (e)      In the event of the death of the Participant or the
                  termination of the Participant's employment by reason of
                  disability or incapacity, then to the extent that the Option
                  was vested and exercisable on the date of the Participant's
                  death or of such termination of employment, it may be
                  exercised by the Participant's personal representative,
                  conservator (if any) or guardian (if any), respectively, for a
                  period of ninety days following the date of the Participant's
                  death or of such termination of employment.

         (f)      The option agreements authorized under the Plan shall contain
                  such other provisions and restrictions as the Committee shall
                  deem advisable.

         (g)      The grant of an option pursuant to the Plan shall not affect
                  in any way the right or power of the Company to make
                  adjustments, reclassifications, reorganizations, or changes of
                  its capital or business structure or to merge or to
                  consolidate or to dissolve, liquidate or sell, or transfer all
                  or any of its business or assets.

         4.       Stock Adjustment: In the event of any stock dividend on,
split-up or combination of, or other change in, the Company's common stock, then
the number or kind of Shares available for option under the Plan or subject to
an option thereunder shall be correspondingly added to, increased, diminished or
changed, without increase or decrease in the aggregate purchase price of all
Shares subject to option before and after such change.

         5.       Administration of Plan: The Committee shall have the power to
interpret the Plan, and to make rules for carrying it out. It shall have no
power (without the consent of the Participant) to change the terms and
conditions of any option except to the extent, if any, provided in such option.
The Board or the Executive Committee of the Board may amend, suspend or
terminate the Plan at any time. No such amendment, suspension or termination
shall affect options then in effect without the consent of the Participant.

                                      -2-

<PAGE>   3

                       MISSISSIPPI VALLEY BANCSHARES, INC.
            1991 NON-QUALIFIED STOCK OPTION PLAN (FIVE-YEAR OPTIONS)

                                OPTION AGREEMENT

         This Option Agreement is entered into effective              , 19  ,
between Mississippi Valley Bancshares, Inc., a Missouri corporation (the
"Company"), and                              (the "Optionee").

         WHEREAS, the Company deems it to be in its best interests to promote
the loyalty and facilitate the retention of certain officers of the Company or
its subsidiaries by offering them an increased incentive, in the form of
proprietary interests in the Company, to continue in the service of the Company
(including its subsidiaries) and increase their efforts for its welfare, and

         WHEREAS, in furtherance of the above purposes the Company has adopted
its 1991 Stock Option Plan (Five-Year Options) (the "Plan"), and desires to
afford the Optionee an opportunity to purchase shares of its common stock
pursuant to the Plan as hereafter described,

         NOW, THEREFORE, in consideration of the premises and for other good and
valuable consideration, the parties hereto do hereby agree as follows:

         1. Grant of Option. The Company hereby grants to the Optionee the right
and option (the "Option") to purchase all or any part of the number of shares of
the Common Stock of the Company set forth below (the "Shares"), at the purchase
price set forth below and on the other terms and conditions herein set forth.

                                TOTAL NUMBER OF SHARES:  ________

                                PURCHASE PRICE PER SHARE:  $_____

         2.       Dates When Option Exercisable.

         (a)      The Option shall vest and first become exercisable as follows:

                                    ___% ON _____________, 20__;

                                    ___% ON _____________, 20__;

                                    ___% ON _____________, 20__; AND

                                    ___% ON _____________, 20__.

         (b) Except as otherwise provided in paragraph 2(e), the Option shall
expire, to the extent it has not already been exercised, at the close of
business on the following date:

                      EXPIRATION DATE: ______________, 20__

         (c) Notwithstanding paragraph 2(a) above, in the event of a Change in
Control, as hereinafter defined, the Option shall immediately vest and become
exercisable in full. For the purpose of this Option, "Change in Control" shall
mean (i) a merger or consolidation of the

<PAGE>   4

Company with or into any other entity after which the holders of the voting
stock of the Company immediately prior to such merger or consolidation do not
own, in substantially the same proportions as they owned the voting stock of the
Company immediately prior to such merger or consolidation, at least a majority
of the voting power of the surviving or resulting entity immediately following
such merger or consolidation, or (ii) any change or changes in the beneficial
ownership of a majority of the Company's voting stock within any one-year
period, including any such change or changes effected in whole or in part by the
redemption of outstanding shares or the issuance of new shares.

         (d) Notwithstanding paragraph 2(a) above, in the event of any
transaction in which the holders of the Company's common stock shall receive or
may elect to receive either cash or securities of an entity other than the
Company, the Option shall vest and become exercisable in full not less than 10
days before the last date upon which the shareholders of the Company eligible to
participate in, and receive the consideration payable in, such transaction is
determined, so as to permit the Optionee to participate in, and receive the
consideration payable in, the transaction with respect to the Shares.

         (e) Notwithstanding paragraph 2(b) and Section 3, in the event of the
death of the Optionee or termination of the Optionee's employment by reason of
his or her disability or incapacity, the Option may be exercised (but only to
the extent it was exercisable by the Optionee immediately prior to his or her
death or such termination of employment), by the Optionee's personal
representative, conservator (if any) or guardian (if any), respectively, in the
manner set forth below, for a period of 90 days after the date of the Optionee's
death or of such termination of employment.

         3. Additional Condition to Exercise. Except as provided in paragraph
2(e), the Option may be exercised only if the Optionee shall have continuously
served as an employee of the Company or its subsidiaries from the date hereof to
and including the date of exercise. It is expressly understood and agreed that
nothing herein is intended or shall be construed as an employment contract or as
implying any obligation on the part of the Company to continue the Optionee's
employment during a period sufficient to permit the Option to vest.

         4. Method of Exercising Option. The Optionee may exercise the Option
hereby granted on one or more occasions at his or her discretion, on each
occasion for all or any part of the Shares for which the Option is then
exercisable, by each time delivering to the Secretary of the Company a written
notice stating his or her election to exercise the Option and the number of
Shares to be purchased, together with cash or check in full payment of the
purchase price of the Shares then purchased, plus the amount of any Federal and
state withholding taxes payable by the Company as a result of such exercise. The
Option shall be deemed to be exercised only upon receipt of such notice and
payment by the Secretary.

         5. Non-Transferability of Option. The Option shall not be transferable,
and may be exercised only by the Optionee or as otherwise provided in paragraph
2(e) or by the Plan. More particularly, but without limiting the generality of
the foregoing, the Option may not be assigned, transferred, pledged or
hypothecated in any way, other than by will or by operation of law and shall not
be subject to execution, attachment or similar process. In the event of the
bankruptcy of the Optionee or in the event of any prohibited assignment,
transfer, pledge, hypothecation or other disposition of the Option, or the levy
of any execution, attachment or similar process upon the Option, the Option
shall automatically expire and shall be null and void.

                                      -2-

<PAGE>   5

         6. Share Adjustments. In the event of any stock dividend on,
reclassification, split-up or combination of, or other change in, the Company's
Common Stock, then the number or kind of Shares available for Option shall be
correspondingly added to, reclassified, increased, diminished or changed
proportionately, without increase or decrease in the aggregate purchase price of
all Shares subject to Option before and after such change.

         7. No Rights of Optionee as Shareholder. The Optionee shall have no
rights respecting this Option or the Shares issuable upon exercise of this
Option, except as expressly set forth herein; and the Optionee shall have no
rights as a shareholder with respect to such Shares until this Option has been
duly exercised in accordance with the terms hereof.

         8. General. The Company shall at all times during the term of the
Option reserve and keep available such number of Shares as will be sufficient to
satisfy the requirements of this Option, and shall pay all original issue and
transfer taxes with respect to the issue and transfer of Shares pursuant hereto
and all other fees and expenses necessarily incurred by the Company incurred in
connection therewith.

         IN WITNESS WHEREOF, the Company and the Optionee have executed this
Option Agreement as of the date first above written.

                               Company:   MISSISSIPPI VALLEY BANCSHARES, INC.

                                          By:
                                             -----------------------------------
ATTEST:                                       President

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

                               Optionee:
                                        ----------------------------------------

                                      -3-

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