<PAGE>
                                                                    Exhibit 10.7


                       THIRD AMENDMENT TO CREDIT AGREEMENT



         THIS THIRD AMENDMENT TO CREDIT AGREEMENT, dated as of June 20, 2003
(this "Amendment"), is by and among BLACK BOX CORPORATION OF PENNSYLVANIA, a
Delaware corporation (the "Borrower"), BLACK BOX CORPORATION, a Delaware
corporation (the "Parent"), the other guarantors to the Credit Agreement
(together with the Parent, the "Guarantors"), the lenders parties to the Credit
Agreement (the "Lenders") and CITIZENS BANK OF PENNSYLVANIA, a national banking
association, as agent for the Lenders (in such capacity, the "Agent") and as
Swingline Lender.

                              W I T N E S S E T H:

         WHEREAS, the Borrower, the Guarantors, the Lenders and the Agent are
parties to a Credit Agreement, dated as of April 4, 2000, and amended by that
certain First Amendment to Credit Agreements, dated as of March 30, 2001 and
that certain Second Amendment to Credit Agreements, dated as of April 3, 2002
(as so amended, the "Credit Agreement"), pursuant to which the Lenders have
agreed, on the terms and subject to the conditions described therein, to make
Loans to the Borrower; and

         WHEREAS, the commitments of the Lenders under the Short Term Credit
Agreement, dated as of April 4, 2000, as amended, among the Borrower, the
Guarantors, the Lenders and the Agent have been terminated; and

         WHEREAS, the Borrower has requested the Lenders and the Agent to make
certain changes to the Credit Agreement; and

         WHEREAS, the Lenders and the Agent are willing to amend the Credit
Agreement as set forth below; and

         WHEREAS, capitalized terms used herein and not otherwise defined shall
have the meanings assigned to them in the Credit Agreement;

         NOW, THEREFORE, in consideration of the premises and of the mutual
covenants herein contained, and intending to be legally bound hereby, the
parties hereto agree as follows:

         SECTION 1. Certain Amendments to Credit Agreement. The Credit Agreement
is hereby amended as follows:

         1.1. Section 1.01 of the Credit Agreement is hereby amended by adding
thereto, in appropriate alphabetical sequence, the following definitions:

                  "Covered Stock Repurchase Amount" shall mean (i) for any
         period of four consecutive fiscal quarters for which the Consolidated
         Leverage Ratio is 1.0 to 1.0 or less, zero and (ii) for any other
         period of four consecutive fiscal quarters, an amount equal to fifty
         percent of purchase price paid by the Parent or any subsidiary for
         purchases of capital stock of the Parent during such period.

                  "Current Maturities of Long Term Indebtedness" shall mean
         amounts becoming due during the period in question of principal of
         Indebtedness for borrowed



<PAGE>

         money other than (i) Indebtedness the original maturity date of which
         is less than one year from the date such Indebtedness was incurred and
         (ii) Indebtedness incurred under revolving credit or line of credit
         facilities to the extent such facilities permit reborrowing after
         repayment.

         1.2. The definition of the term "Consolidated Fixed Charge Coverage
Ratio" appearing in Section 1.01 of the Credit Agreement is hereby amended to
read in its entirety as follows:

                  "Consolidated Fixed Charge Coverage Ratio", as of the last day
         of any fiscal quarter, shall mean the ratio of (a) Consolidated EBITDA
         plus the aggregate amounts that were paid as rent by the Parent and its
         consolidated Subsidiaries minus Capital Expenditures of the Parent and
         its consolidated Subsidiaries minus charges against income for foreign,
         federal, state and local income Taxes of the Parent and its
         consolidated Subsidiaries to (b) Current Maturities of Long Term
         Indebtedness of the Parent and its consolidated Subsidiaries plus
         Consolidated Interest Expense plus the aggregate amounts that were paid
         as rent by the Parent and its consolidated Subsidiaries plus the
         aggregate amount of dividends and distributions on the shares of
         capital stock of the Parent plus the Covered Stock Repurchase Amount,
         in each case for the four most recently completed fiscal quarters
         ending on such day, considered as a single accounting period. If an
         Acquisition occurs during such period, each element of the Consolidated
         Fixed Charge Coverage Ratio shall be calculated on a pro forma basis as
         if the Acquisition had been made, and any Indebtedness or other
         obligations issued or incurred in connection therewith had been issued
         or incurred, as of the first day of such period; provided, however,
         that, in making such calculations, the Borrower may ignore those
         expenses and distributions of the acquired Person that would not have
         been incurred had the Acquisition occurred as of the first day of such
         period. In making such pro forma calculation of the Consolidated
         Interest Expense with respect to Indebtedness or other obligations
         issued or incurred in connection with the Acquisition, interest expense
         thereon shall be calculated on the basis of an interest rate per annum
         not less than the one-month Euro-Rate as of the last day of such period
         plus an Applicable Margin determined on the basis of the Consolidated
         Leverage Ratio as of the last day of such period.

         1.3. Section 7.02 of the Credit Agreement is hereby amended to read in
its entirety as follows:

                  7.02. Leverage. As of the last day of each fiscal quarter, the
         Consolidated Leverage Ratio shall no be greater than 2.0 to 1.0.

         1.4. The definition of the term "Prime Rate" appearing in Section 1.01
of the Credit Agreement is hereby amended by deleting the phrase "Mellon Bank,
N. A." each place it appears in such definition and inserting in lieu thereof
the phrase "Citizens Bank of Pennsylvania".

         SECTION 3. Miscellaneous.

         3.1. Effect of Amendment. This Amendment shall become effective upon
(a) the execution by the Borrower, the Guarantors, the Required Lenders and the
Agent, and delivery to the Agent, of this Amendment and (b) receipt by the Agent
of such other certificates, corporate documents and other documents as the Agent
may request. The Credit Agreement, as amended by this Amendment, is in all
respects ratified, approved and confirmed and shall, as so amended, remain in
full force and effect.


<PAGE>

         3.2. Confirmation of Guaranty. Each of the Guarantors reaffirms the
terms and conditions of the Loan Documents executed by it and acknowledges and
agrees that such Loan Documents remain in full force and effect and are hereby
ratified, reaffirmed and confirmed.

         3.3. Governing Law. This Amendment shall be governed by and construed
in accordance with the laws of the Commonwealth of Pennsylvania without giving
effect to the conflict of law principles thereof.

         3.4. Counterparts. This Amendment may be executed in any number of
counterparts and by the different parties hereto on separate counterparts, each
of which, when so executed, shall be deemed an original, but all such
counterparts shall constitute but one and the same instrument.


                                         [SIGNATURES BEGIN ON NEXT PAGE]



<PAGE>



          SIGNATURE PAGE 1 OF 10 TO THIRD AMENDMENT TO CREDIT AGREEMENT
                       WITH BLACK BOX CORPORATION ET AL.



         IN WITNESS WHEREOF, the parties hereto, by their officers thereunto
duly authorized, have executed and delivered this Amendment as of the date first
above written.



                                        BORROWER:

                                        BLACK BOX CORPORATION OF PENNSYLVANIA


                                        By:
                                            -----------------------------------

                                        Name:
                                              ---------------------------------

                                        Title:
                                               --------------------------------



                                        GUARANTORS:

                                        BLACK BOX CORPORATION and each of the
                                        DOMESTIC SUBSIDIARIES listed on Annex A
                                        attached hereto and made a part hereof

                                        By:
                                            -----------------------------------

                                        Name:
                                              ---------------------------------

                                        Title:
                                               --------------------------------

                                                of Black Box Corporation and of
                                                each of the Domestic
                                                Subsidiaries listed on Annex C
                                                hereto





<PAGE>



        SIGNATURE PAGE 2 OF 10 TO TO THIRD AMENDMENT TO CREDIT AGREEMENT
                        WITH BLACK BOX CORPORATION ET AL.

                                        AGENT:

                                        CITIZENS BANK OF PENNSYLVANIA


                                        By:
                                            -----------------------------------

                                        Name:
                                              ---------------------------------

                                        Title:
                                               --------------------------------




                                        BANKS:

                                        CITIZENS BANK OF PENNSYLVANIA

                                        By:
                                            -----------------------------------

                                        Name:
                                              ---------------------------------

                                        Title:
                                               --------------------------------





<PAGE>



         SIGNATURE PAGE 3 OF 10 TO THIRD AMENDMENT TO CREDIT AGREEMENT
                        WITH BLACK BOX CORPORATION ET AL.



                                        WACHOVIA BANK, NATIONAL ASSOCIATION

                                        By:
                                            -----------------------------------

                                        Name:
                                              ---------------------------------

                                        Title:
                                               --------------------------------




<PAGE>



         SIGNATURE PAGE 4 OF 10 TO THIRD AMENDMENT TO CREDIT AGREEMENT
                        WITH BLACK BOX CORPORATION ET AL.


                                        FLEET NATIONAL BANK

                                        By:
                                            -----------------------------------

                                        Name:
                                              ---------------------------------

                                        Title:
                                               --------------------------------






<PAGE>



         SIGNATURE PAGE 5 OF 10 TO THIRD AMENDMENT TO CREDIT AGREEMENT
                        WITH BLACK BOX CORPORATION ET AL.



                                        NATIONAL CITY BANK OF PENNSYLVANIA

                                        By:
                                            -----------------------------------

                                        Name:
                                              ---------------------------------

                                        Title:
                                               --------------------------------




<PAGE>



         SIGNATURE PAGE 6 OF 10 TO THIRD AMENDMENT TO CREDIT AGREEMENT
                        WITH BLACK BOX CORPORATION ET AL.



                                        COMERICA BANK

                                        By:
                                            -----------------------------------

                                        Name:
                                              ---------------------------------

                                        Title:
                                               --------------------------------




<PAGE>



        SIGNATURE PAGE 7 OF 10 TO TO THIRD AMENDMENT TO CREDIT AGREEMENT
                        WITH BLACK BOX CORPORATION ET AL.



                                        FIRSTAR BANK, N.A.

                                        By:
                                            -----------------------------------

                                        Name:
                                              ---------------------------------

                                        Title:
                                               --------------------------------




<PAGE>



         SIGNATURE PAGE 8 OF 10 TO THIRD AMENDMENT TO CREDIT AGREEMENT
                       WITH BLACK BOX CORPORATION ET AL.



                                        KEYBANK NATIONAL ASSOCIATION

                                        By:
                                            -----------------------------------

                                        Name:
                                              ---------------------------------

                                        Title:
                                               --------------------------------



<PAGE>



         SIGNATURE PAGE 9 OF 10 TO THIRD AMENDMENT TO CREDIT AGREEMENT
                       WITH BLACK BOX CORPORATION ET AL.



                                        MELLON BANK, N. A.

                                        By:
                                            -----------------------------------

                                        Name:
                                              ---------------------------------

                                        Title:
                                               --------------------------------




<PAGE>



         SIGNATURE PAGE 10 OF 10 TO THIRD AMENDMENT TO CREDIT AGREEMENT
                       WITH BLACK BOX CORPORATION ET AL.



                                        FIFTH THIRD BANK

                                        By:
                                            -----------------------------------

                                        Name:
                                              ---------------------------------

                                        Title:
                                               --------------------------------





<PAGE>



                 ANNEX A TO THIRD AMENDMENT TO CREDIT AGREEMENT

                       GUARANTORS - DOMESTIC SUBSIDIARIES



BBox Holding Company
Atimco Network Services, Inc.
American Telephone Wiring Company
Midwest Communications Technologies, Inc.
Associated Network Solutions, Inc.
Advanced Communications Corporation
Cable Consultants, Incorporated
Todd Communications, Inc.
Comm Line, Inc.
Business Communications Concepts, Inc.
Koncepts Communications of L.I., Corp.
Communication Contractors, Inc.
DataCom-Link, Inc.
U.S. Premise Networking Services, Inc.
TennMark Telecommunications, Inc.
Parrish Communications Cabling, Inc.
R&D Services, Inc.
Delaney Telecom, Inc.
Delaney Electrical Services, Inc.
K&A Communications, Inc.
Jet Line Communications, Inc.
A.T.S., Inc.
Coast to Coast Communications, Inc.
Advanced Network Technologies, Inc.
BB Technologies, Inc.