<PAGE>   1
                                                                   EXHIBIT 4.7.1

                          FIRST AMENDMENT TO INDENTURE

         THIS FIRST AMENDMENT to the Indenture, dated as of March 24, 1997, by
and among Key Plastics, Inc., a Michigan corporation, as Issuer (the "Company"),
Key Plastics International LLC, a Michigan limited liability company, Key
Plastics Automotive LLC, a Michigan limited liability company, Key Plastics
Technology, LLC, a Michigan limited liability company, Key Mexico A, LLC, a
Michigan limited liability company and Key Mexico B, a Michigan limited
liability company, as Guarantors (the "Guarantors") and Marine Midland Bank, as
Trustee (the "Trustee") is made as of the 9th day of February, 1998 by and among
the Company, the Guarantors and the Trustee.

         Section 9.01 of the Indenture provides, among other things, that the
Company and the Guarantors, when authorized by a Board Resolution (such term and
all other capitalized terms used and not defined herein shall have the meanings
assigned to such terms in the Indenture), and the Trustee may amend the
Indenture, without the consent of any Holder of a Senior Subordinated Note, for
certain purposes, as set forth therein. This Amendment is being entered into for
the purposes set forth in Section 9.01(a), has been duly authorized by the Board
of Directors of the Company and each of the Guarantors, and the Trustee has
received such other documents as required by Section 9.01 in order to authorize
the Trustee to enter into this Amendment.

         Accordingly, the parties hereto hereby agree as follows:

SECTION 1.        AMENDMENTS TO THE INDENTURE

                                    ARTICLE 1
                          DEFINITIONS AND INCORPORATION
                                  BY REFERENCE

         (a) Section 1.01 of the Indenture is hereby amended by deleting the
definition of "Board of Directors" and substituting therefore the following:

         "Board of Directors" means the Board of Directors or Management
Committee of the Company, or any authorized committee of the Board of Directors
or authorized subcommittee of the Management Committee.

         (b) Section 1.01 of the Indenture is amended by deleting the definition
of "Change of Control" and substituting therefore the following:

         "Change of Control" means the occurrence of any of the following: (i)
the adoption of a plan relating to the liquidation or dissolution of the
Company, (ii) the consummation of any transaction (including, without
limitation, any merger or consolidation) the result of which is that (a) prior
to an Initial Public Offering, any "Person" (as such term is used in Section
13(d)(3) of


<PAGE>   2



the Exchange Act), other than the Principals and their Related Parties, (1)
becomes the "beneficial owner" (as such term is defined in Rule 13d-3 and Rule
13d-5 under the Exchange Act, except that a Person shall be deemed to have
"beneficial ownership" of all securities that such Person has the right to
acquire, whether such right is currently exercisable or is exercisable only upon
the occurrence of a subsequent condition), directly or indirectly, of more than
50% of the Voting Stock of the Company (measured by voting power rather than
number of shares), (2) becomes a shareholder of the Company with the right to
appoint or remove directors of the Company holding 50% or more of the voting
rights at meetings of the Board of Directors on all, or substantially all,
matters or (3) becomes able to exercise the right to give directions with
respect to the operating and financial policies of the Company with which the
relevant directors are obligated to comply by reason of (A) provisions contained
in the organization documents of the Company, or (B) the existence of any
contract permitting such Person to exercise control over the Company, or (b)
after an Initial Public Offering, any "Person" (as defined above), other than
the Principals and their Related Parties, becomes the "beneficial owner" (as
such term is defined in Rule 13d-3 and Rule 13d-5 under the Exchange Act, except
that a Person shall be deemed to have "beneficial ownership" of all securities
that such Person has the right to acquire, whether such right is currently
exercisable or is exercisable only upon the occurrence of a subsequent
condition), directly or indirectly, of more than 30% of the total of the Voting
Stock of the Company (measured by voting power rather than number of shares),
and, the Principals, collectively, are the "beneficial owners" of a lesser
percentage of the Voting Stock of the Company than such other "Person" and do
not have the right or ability by voting power, contract or otherwise, to elect
or designate for election, a majority of the Board of Directors of the Company,
(iii) the first day on which a majority of the members of the Board of Directors
of the Company are not Continuing Directors, (iv) the Company consolidates with,
or merges with or into, any Person or the Company and its Subsidiaries taken as
a whole sells, assigns, conveys, transfers, leases or otherwise disposes of all
or substantially all of its assets to any Person, or any Person consolidates
with, or merges with or into, the Company, in any such event pursuant to a
transaction in which any of the outstanding Voting Stock of the Company is
converted into or exchanged for cash, securities or other property, other than
any such transaction where the Voting Stock of the Company outstanding
immediately prior to such transaction is converted into or exchanged for Voting
Stock (other than Disqualified Stock) of the surviving or transferee Person
constituting a majority of the outstanding shares of such Voting Stock of such
surviving or transferee Person (immediately after giving effect to such
issuance) or (v) the Company and its Subsidiaries taken as a whole sells,
assigns, conveys, transfers, leases or otherwise disposes of all or
substantially all of its assets to any Person pursuant to a transaction in which
none of the outstanding Voting Stock of the Company is converted into or
exchanged for cash, securities or other property.

                                    ARTICLE 5
                                   SUCCESSORS

         (a) Article 5 of the Indenture is hereby amended by deleting Article 5
in its entirety and substituting therefore the following:

                                        2

<PAGE>   3



Section 5.01.     Merger, Consolidation, or Sale of Assets.

                  The Company shall not consolidate or merge with or into
(whether or not the Company is the surviving Person), or sell, assign, transfer,
lease, convey or otherwise dispose of all or substantially all of its properties
or assets in one or more related transactions, to another Person unless (i) the
Company is the surviving Person or the Person formed by or surviving any such
consolidation or merger (if other than the Company) or to which such sale,
assignment, transfer, lease, conveyance or other disposition shall have been
made is a Person organized or existing under the laws of the United States, any
state thereof or the District of Columbia; (ii) the Person formed by or
surviving any such consolidation or merger (if other than the Company) or the
Person to which such sale, assignment, transfer, lease, conveyance or other
disposition shall have been made assumes all the obligations of the Company
under the Senior Subordinated Notes and this Indenture pursuant to a
supplemental indenture in a form reasonably satisfactory to the Trustee; (iii)
immediately after such transaction no Default or Event of Default exists; (iv)
except in the case of a merger of the Company with or into a Guarantor, the
Company or Person formed by or surviving any such consolidation or merger (if
other than the Company), or to which such sale, assignment, transfer, lease,
conveyance or other disposition shall have been made (A) will have Consolidated
Net Worth immediately after the transaction equal to or greater than the
Consolidated Net Worth of the Company immediately preceding the transaction and
(B) will, at the time of such transaction and after giving pro forma effect
thereto as if such transaction had occurred at the beginning of the applicable
four-quarter period, be permitted to incur at least $1.00 of additional
Indebtedness pursuant to the Fixed Charge Coverage Ratio test set forth in the
first paragraph of Section 4.09; and (v) the Company has delivered to the
Trustee an Officers' Certificate and an Opinion of Counsel, each stating that
such consolidation, merger, sale, assignment, transfer, lease, conveyance or
other disposition and such supplemental indenture complies with this Article and
that all conditions precedent herein provided for relating to such transaction
have been complied with.

Section 5.02.     Successor Corporation Substituted.

                  Upon any consolidation or merger, or any sale, assignment,
transfer, lease, conveyance or other disposition of all or substantially all of
the assets of the Company in accordance with Section 5.01 hereof, the successor
Person formed by such consolidation or into or with which the Company is merged
or to which such sale, assignment, transfer, lease, conveyance or other
disposition is made shall succeed to, and be substituted for (so that from and
after the date of such consolidation, merger, sale, lease, conveyance or other
disposition, the provisions of this Indenture referring to the "Company" shall
refer instead to the successor Person and not to the Company), and may exercise
every right and power of the Company under this Indenture with the same effect
as if such successor Person had been named as the Company herein; provided,
however, that the predecessor Company shall not be relieved from the obligation
to pay the principal of and interest on the Senior Subordinated Notes except in
the case of a sale of all of the Company's assets that meets the requirements of
Section 5.01 hereof.


                                        3

<PAGE>   4



Section 2.        GOVERNING LAW.

         THE INTERNAL LAW OF THE STATE OF NEW YORK SHALL GOVERN AND BE USED TO
CONSTRUE THIS AMENDMENT.

Section 3.        HEADINGS

         The Headings of the Sections of this Amendment have been inserted for
convenience of reference only, are not to be considered a part of this Amendment
and shall in no way modify or restrict any of the terms or provisions hereof.

Section 4.        COUNTERPART ORIGINALS.

         The parties may sign any number of copies of this Amendment. Each
signed copy shall be an original, but all of them together represent the same
agreement.

Section 5.        THE TRUSTEE.

         The Trustee shall not be responsible in any manner whatsoever for or in
respect of the validity or sufficiency of this Amendment or for or in respect of
the recitals contained herein, all of which recitals are made solely by the
Company and the Guarantors.

IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be duly
executed and attested, all as of the date first written above.

                                  KEY PLASTICS, INC.


                                  By: /s/ Mark J. Abbo
                                     ----------------------------
                                    Name:  Mark J. Abbo
                                    Title:    Treasurer and Assistant Secretary

                                  KEY PLASTICS INTERNATIONAL LLC

                                  By:  Key Plastics, Inc.,


                                  By:  /s/ Mark J. Abbo
                                     ----------------------------
                                    Name:  Mark J. Abbo
                                    Title:    Treasurer and Assistant Secretary



                                        4

<PAGE>   5



                                  KEY PLASTICS AUTOMOTIVE LLC

                                  By:  Key Plastics, Inc., a Member



                                  By:  /s/ Mark J. Abbo
                                     ---------------------
                                    Name:  Mark J. Abbo
                                    Title:    Treasurer and Assistant Secretary

                                  KEY PLASTICS TECHNOLOGY LLC

                                  By:  Key Plastics, Inc., a Member



                                  By: /s/ Mark J. Abbo
                                     ---------------------
                                    Name:  Mark J. Abbo
                                    Title:    Treasurer and Assistant Secretary

                                  KEY MEXICO A, LLC

                                  By:  Key Plastics, Inc., a Member



                                  By: /s/ Mark J. Abbo
                                     ---------------------
                                    Name:  Mark J. Abbo
                                    Title:    Treasurer and Assistant Secretary

                                  KEY MEXICO B, LLC

                                  By:  Key Plastics, Inc., a Member



                                  By:  /s/ Mark J. Abbo
                                     ---------------------
                                    Name:  Mark J. Abbo
                                    Title:    Treasurer and Assistant Secretary





                                        5

<PAGE>   6


                                  MARINE MIDLAND BANK, as Trustee



                                  By: /s/ Marcia Markowski
                                     ------------------------
                                    Name:  Marcia Markowski
                                         --------------------
                                    Title: Assistant Vice President
                                          -------------------------


                                        6