<PAGE>
                                                                    Exhibit 10.5
================================================================================
FIFTH AMENDMENT TO
AMENDED AND RESTATED LOAN AND SECURITY AGREEMENT
169784.4
================================================================================

                                                                 October 1, 1996
                                                    Effective: September 4, 1996

     THIS FIFTH AMENDMENT IS made to the Amended and Restated Loan and Security
Agreement (the "Loan Agreement"), which Amended and Restated Loan and Security
Agreement took effect on April 6, 1995 as an amendment and restatement of the
December 16, 1994 Loan and Security Agreement made between

           The First National Bank of Boston, a national banking association
     with offices at 100 Federal Street, Boston, Massachusetts, as agent for the
     ratable benefit of the "Lenders" being:

                The First National Bank of Boston;

                        and

                State Street Bank and Trust Company, a Massachusetts trust
                company with offices at 225 Franklin Street, Boston,
                Massachusetts 02110;

                        and

                Citizens Bank of Massachusetts, a Massachusetts savings bank
                with offices at 55 Summer Street, Boston, Massachusetts 02110

           and

           ACT Manufacturing, Inc., a Massachusetts corporation with its
     principal executive offices at 108 Forest Avenue, Hudson, Massachusetts
     01749

in consideration of the mutual covenants contained herein and benefits to be
derived herefrom,

                                  WITNESSETH:

<PAGE>
 
     1.   AGREEMENT TO AMEND
          ------------------
 
     Provided each of those "Conditions to Amendment" set forth in Section 2,
below, is satisfied on or before September 24, 1996, the Loan Agreement shall be
amended, as set forth below, such amendment to take effect as of September 4,
1996.

     Section 1-1 of the Loan Agreement (Section Preceeding Section 1-1(a) is
          amended to read as follows:

     The Lenders hereby severally (and not jointly) establish a revolving line
of credit (hereinafter, the "Revolving Credit") in the Borrower's favor pursuant
to which each Lender, subject to, and in accordance with, the within Agreement,
and acting through the Agent, shall make loans and advances (each, a "Revolving
Credit Loan") to and for the account of the Borrower as provided herein, in each
instance equal to that Lender's Commitment Percentage (defined below) of the
subject Tranche of the Revolving Credit up to the maximum amount of that
Lender's Commitment (defined below) applicable to that Tranche. The amount of
the Revolving Credit shall be determined by the Agent by reference to
Availability (as defined below), as determined by the Agent from time to time
hereafter.  All loans made by the Lenders under this Agreement, and all of the
Borrower's other Liabilities (as defined below) to the Lenders under or pursuant
to this Agreement, are payable as provided herein.

     Section 1-1(d) of the Loan Agreement (Definition of "Loan Cap") is amended
          to read as follows:
<TABLE>
<CAPTION>
 
     "Loan Cap": The following amount between the dates indicated, then
          aggregate Stated Minus, in each instance, the Amount of all L/C's:
--------------------------------------------------------------------------------
From                         To                       Loan Cap
--------------------------------------------------------------------------------
<S>                          <C>                      <C>
September 4, 1996            October 18, 1996         $32,000,000.00
--------------------------------------------------------------------------------
October 19, 1996             Termination Date         $28,000,000.00
--------------------------------------------------------------------------------
</TABLE>
     Section 1-1 of the Loan Agreement is amended by the addition of the
          following Section:

          (e)   During the period September 4, 1996 to October 18, 1996, the
Revolving Credit shall be divided into two tranches, as follows:

                "Tranche A":  The first $28,000,000.00.
                "Tranche B":  In excess of $28,000,000.00 to the Loan Cap.

<PAGE>
 
     Section 1-8 of the Loan Agreement is amended by the addition of the
          following Section:

          (e) All repayments of principal made pursuant to this Section shall be
applied first to any unpaid principal balance of Tranche B and then to any
unpaid principal balance of Tranche A.


     Article 3 is amended by the amendment of the following definitions,
          included therein, to read as follows:

     "Commitment and Commitment Percentage": the following amounts and
          Percentages during the periods indicated:
<TABLE>
<CAPTION>
================================================================================
REVOLVING CREDIT:
COMMITMENTS AND PERCENTAGE COMMITMENTS
================================================================================
LENDER
================================================================================
                                                                             
                            DOLLAR COMMITMENT       COMMITMENT                 
                            TO REVOLVING CREDIT     PERCENTAGE OF              
                            LOANS                   REVOLVING                  
                            ($ MILLIONS)            CREDIT LOANS               
                            ===================================================
                            Tranche A  Tranche B    Tranche A    Tranche B
-------------------------------------------------------------------------------
<S>                          <C>        <C>        <C>         <C>
THE FIRST NATIONAL BANK           16.8        3.0         60%              75%
OF BOSTON
-------------------------------------------------------------------------------
STATE STREET                       5.6        1.0         20%              25%
-------------------------------------------------------------------------------
CITIZENS                           5.6        -0-         20%              -0-

-------------------------------------------------------------------------------
  TOTALS.....................    $28.0       $4.0        100%
===============================================================================
</TABLE> 

     2.  CONDITIONS TO EFFECTIVENESS OF AMENDMENT
         ----------------------------------------

     The within Amendment shall be effective if each of the following conditions
is satisfied on or before September 24, 1996 and on the date on which such
amendment is to take effect, no Suspension Event (as defined in the Loan
Agreement) is extant:
 
         (a) Receipt by the Agent of a Certificate setting forth the text of the
resolutions adopted by the Directors of the Borrower authorizing the

<PAGE>
 
Borrower's execution of the within Amendment, and attesting to the authority of
the persons who executed the within Amendment on behalf of the Borrower. 
 
         (b) Receipt by the Agent of a Certificate, executed by the Borrower's
President and its Chief Financial Officer, respectively confirming that no
Suspension Event is then extant. 
 
         (c) Receipt by the Agent of an opinion of counsel to the Borrower as to
the due execution and effectiveness of the within Amendment (which opinion is
subject only to the same qualifications as had been included in the opinion
delivered by that counsel at the initial execution of the Loan Agreement).
 
         (d) Receipt by the Agent of an Amendment Fee of $7,500.00, which fee,
the Agent shall distribute to the Lenders in accordance with the terms of the
Agency Agreement, as amended, between the Lenders, on the one hand, and the
Agent, on the other. 

     The Borrower hereby represents that, at the execution of the within
Agreement, no Suspension Event has occurred.

<PAGE>
 
     Except as amended hereby, or by the First, Second, Third, and Fourth
Amendments to the Loan Agreement, all terms and conditions of the Loan Agreement
shall remain in full force and effect.
 


                                ACT MANUFACTURING, INC.
                                              (The "Borrower")

                                By /s/ Douglass C. Greenlaw
                                  --------------------------------

                                Its Chief Financial Officer
                                   -------------------------------


THE FIRST NATIONAL BANK OF BOSTON
                    ("Agent")

By /s/ George Mandt
  --------------------------------

Its Vice President
   -------------------------------

                                 The "Lenders"

THE FIRST NATIONAL BANK                  STATE STREET BANK  
OF BOSTON                                AND TRUST COMPANY 

By  /s/ George Mandt                     By /s/ F. Andrew Beise
  --------------------------------         --------------------------------

Its Vice President                       Its Vice President
   -------------------------------          -------------------------------

CITIZENS BANK OF MASSACHUSETTS

By /s/ Anne Forbes Van Nest
  -------------------------------- 

Its  Vice President
   -------------------------------