<PAGE>


                                                                EXHIBIT 4.6

               FOURTH SUPPLEMENTAL INDENTURE TO SERIES B INDENTURE
               SECOND SUPPLEMENTAL INDENTURE TO SERIES D INDENTURE

         Fourth Supplemental Indenture to the Series B Indenture (as defined 
below) and Second Supplemental Indenture to the Series D Indenture (as 
defined below), dated as of June 1, 1998 (this "Supplemental Indenture"), 
among Aftermarket Technology Corp., a Delaware corporation (the "Company"), 
the Guarantors named herein and Firstar Bank of Minnesota, N.A., formerly 
known as American Bank National Association, as Trustee

         Each party hereto agrees as follows for the benefit of each other 
party and for the equal and ratable benefit of the Holders of the Company's 
12% Series B Senior Subordinated Notes due 2004 (the "Series B Notes") and 
the Holders of the Company's 12% Series D Senior Subordinated Notes due 2004 
(the "Series D Notes"). All capitalized terms used in this Supplemental 
Indenture and not defined herein shall have the meanings specified in the 
Indentures (defined below).

         WHEREAS, the Company, the Trustee, and each of the Guarantors other 
than ACI Electronics Holding Corp., a Delaware corporation ("ACI Holding"), 
ACI Electronics Investment Corp., a Delaware corporation ("ACI Investment"), 
Aftermarket Technology (U.K.) Holdings Limited, a United Kingdom company 
("U.K. Holdings"), ATC Distribution Group, Inc., a Delaware corporation 
("ATCDG"), ATC Electronics & Logistics, L.P., a Delaware limited partnership 
("ATC Electronics"), ATS Remanufacturing, Inc., a Delaware corporation 
("ATS"), Autocraft Industries, Inc., a Delaware corporation ("Autocraft 
Industries"), Autocraft Remanufacturing Corp., a Delaware corporation 
("Autocraft Remanufacturing"), Automotive Developments Limited, a United 
Kingdom company ("ADL"), and Metran Automatic Transmission Parts, Corp., a 
New York corporation ("Metran"), have entered into (i) that certain 
Indenture, dated as of August 2, 1994, as supplemented by the First 
Supplemental Indenture, dated as of February 23, 1995, the Second 
Supplemental Indenture, dated as of June 1, 1995, and the Third Supplemental 
Indenture, dated as of June 25, 1996, relating to the issuance of the Series 
B Notes (the "Series B Indenture") and (ii) that certain Indenture, dated as 
of June 1, 1995, as supplemented by the First Supplemental Indenture, dated 
as of June 25, 1996, relating to the issuance of the Series D Notes (the 
"Series D Indenture" and, collectively with the Series B Indenture, the 
"Indentures").

         WHEREAS, pursuant to the terms of each of the Indentures, the 
Company and the Guarantors have covenanted and agreed that they shall cause 
each person that is or becomes a Subsidiary of the Company or any Guarantor 
to execute a Guaranty and to cause such Subsidiary to execute an indenture 
supplement to the Indentures for the purpose of adding such Subsidiary as a 
Guarantor under the Indentures;

         WHEREAS, ACI Holding, ACI Investment, U.K. Holdings, ATCDG, ATC 
Electronics, ATS, Autocraft Industries, Autocraft Remanufacturing, ADL and 
Metran (collectively, the "New Subsidiaries"), each of which is a Subsidiary 
of the Company or a Guarantor, are not currently included as Guarantors in 
the Indentures;

         WHEREAS, the parties hereto desire that the New Subsidiaries assume 
the rights, duties and obligations of a Guarantor under the Indentures;

<PAGE>

         WHEREAS, all things necessary to make this Supplemental Indenture a 
valid, binding and legal instrument supplemental to the Indentures have been 
performed;

         NOW, THEREFORE, THIS INDENTURE WITNESSETH: that, in consideration of 
the covenants and premises, receipt whereof is hereby acknowledged, each of 
the New Subsidiaries (i) hereby agrees and provides, for the equal and 
proportionate benefit of the respective Holders, that each of the New 
Subsidiaries hereby assumes the rights, duties and obligations of a Guarantor 
under the Indentures, as amended hereby, including without limitation the 
execution of a Guaranty in the form attached hereto, and (ii) shall be bound 
by the terms and conditions of the Indentures, as amended hereby, as if the 
New Subsidiaries were originally parties hereto.

         IN WITNESS WHEREOF, the parties hereto have caused this Supplemental 
Indenture to be duly executed as of the date first written above.

                                       AFTERMARKET TECHNOLOGY CORP.


                                       By:    /S/ JOHN C. KENT
                                             -------------------
                                                 John C. Kent
                                            Chief Financial Officer

Attest:


         /S/ JOSEPH SALAMUNOVICH
     ------------------------------
     Joseph Salamunovich, Secretary



                                       FIRSTAR BANK OF MINNESOTA, N.A.,
                                       As Trustee

                                       By: /S/ FRANK LESLIE
                                           ----------------
                                             Frank Leslie
                                            Vice President


<PAGE>

                                       THE "GUARANTORS":

                                       AARON'S AUTOMOTIVE PRODUCTS, INC.
                                       a Delaware corporation

                                       By:   /S/ JOSEPH SALAMUNOVICH
                                             -----------------------
                                               Joseph Salamunovich
                                                 Vice President


                                       ACI ELECTRONICS HOLDING CORP.
                                       a Delaware corporation

                                       By:   /S/ JOSEPH SALAMUNOVICH
                                             -----------------------
                                               Joseph Salamunovich
                                                 Vice President


                                       ACI ELECTRONICS INVESTMENT CORP.
                                       a Delaware corporation

                                       By:   /S/ JOSEPH SALAMUNOVICH
                                             -----------------------
                                               Joseph Salamunovich
                                                 Vice President


                                       AFTERMARKET TECHNOLOGY (U.K.) HOLDINGS
                                       LIMITED
                                       a United Kingdom company

                                       By:   /S/ JOSEPH SALAMUNOVICH
                                             -----------------------
                                               Joseph Salamunovich
                                                    Director


                                       ATC DISTRIBUTION GROUP, INC.
                                       a Delaware corporation

                                       By:  /S/ JOSEPH SALAMUNOVICH
                                            -----------------------
                                             Joseph Salamunovich
                                                Vice President

<PAGE>

                                       ATC ELECTRONICS & LOGISTICS, L.P.
                                       a Delaware limited partnership

                                       By:  ACI Electronics Holding Corp.,
                                            general partner

                                       By: /S/ JOSEPH SALAMUNOVICH
                                           ----------------------
                                            Joseph Salamunovich
                                               Vice President


                                       ATS REMANUFACTURING, INC.
                                       a Delaware corporation

                                       By: /S/JOSEPH SALAMUNOVICH
                                           ----------------------
                                            Joseph Salamunovich
                                              Vice President


                                       AUTOCRAFT INDUSTRIES, INC.
                                       a Delaware corporation

                                       By: /S/ JOSEPH SALAMUNOVICH
                                           ----------------------
                                            Joseph Salamunovich
                                               Vice President


                                       AUTOCRAFT REMANUFACTURING CORP.
                                       a Delaware corporation

                                       By: /S/JOSEPH SALAMUNOVICH
                                           ----------------------
                                            Joseph Salamunovich
                                               Vice President


                                       AUTOMOTIVE DEVELOPMENTS LIMITED
                                       a United Kingdom company

                                       By: /S/ JOSEPH SALAMUNOVICH
                                           -----------------------
                                            Joseph Salamunovich
                                                 Director


                                       COMPONENT REMANUFACTURING
                                       SPECIALISTS, INC.
                                       a New Jersey corporation

                                       By: /S/ JOSEPH SALAMUNOVICH
                                           -----------------------
                                            Joseph Salamunovich
                                               Vice President

<PAGE>

                                       CRS HOLDINGS, INC.
                                       a New Jersey corporation

                                       By: /S/ JOSEPH SALAMUNOVICH
                                           -----------------------
                                             Joseph Salamunovich
                                               Vice President


                                       KING-O-MATIC INDUSTRIES LIMITED,
                                       an Ontario corporation

                                       By: /S/ JOSEPH SALAMUNOVICH
                                           -----------------------
                                             Joseph Salamunovich
                                               Vice President


                                       MASCOT TRUCK PARTS, INC.
                                       an Ontario corporation

                                       By:  /S/ JOSEPH SALAMUNOVICH
                                           -----------------------
                                             Joseph Salamunovich
                                               Vice President

                                       METRAN AUTOMATIC TRANSMISSION PARTS CORP.
                                       a Delaware corporation

                                       By: /S/ JOSEPH SALAMUNOVICH
                                           -----------------------
                                            Joseph Salamunovich
                                              Vice President


                                       PARTES REMANUFACTURADES DE
                                       MEXICO, S.A. DE C.V.
                                       a Mexico corporation

                                       By:  /S/ JOSEPH SALAMUNOVICH
                                           -----------------------
                                             Joseph Salamunovich
                                               Vice President


                                       RPM MERIT, INC.,
                                       a Delaware corporation


                                       By:  /S/ JOSEPH SALAMUNOVICH
                                           -----------------------
                                             Joseph Salamunovich
                                               Vice President

<PAGE>


                                    GUARANTY

For value received, ________________, a ______________ corporation, hereby
unconditionally guarantees to the Holder of the security upon which this
guaranty is endorsed the due and punctual payment, as set forth in the Indenture
pursuant to which such Security and this Guaranty were issued, of the principal
of, premium (if any) and interest on such Security when and as the same shall
become due and payable for any reason according to the terms of such Security
and Article XIII of the Indenture. The Guaranty of the Security upon which this
Guaranty is endorsed will not become effective until the Trustee signs the
certificate of authentication on such Security.

                                           ________________________________
                                           a ______________ corporation


                                           By:  ______________________________
                                           Name:
                                           Title: