1
 
                                                                    Exhibit 99.3
 
                    INSTRUCTIONS TO REGISTERED HOLDER AND/OR
         BOOK-ENTRY TRANSFER FACILITY PARTICIPANT FROM BENEFICIAL OWNER
                                       OF
                           STANADYNE AUTOMOTIVE CORP.
                   10 1/4% SENIOR SUBORDINATED NOTES DUE 2007
 
     To Registered Holder and/or Participant of the Book-Entry Transfer
Facility:
 
     The undersigned hereby acknowledges receipt of the Prospectus, dated
          , 1998 (the "Prospectus"), of Stanadyne Automotive Corp., a Delaware
corporation (the "Company"), and the accompanying Letter of Transmittal (the
"Letter of Transmittal"), that together constitute the Company's offer (the
"Exchange Offer"). Capitalized terms used but not defined herein have the
meanings ascribed to them in the Prospectus.
 
     This will instruct you, the registered holder and/or book-entry transfer
facility participant, as to action to be taken by you relating to the Exchange
Offer with respect to the 10 1/4% Senior Subordinated Notes due 2007 (the
"Notes") held by you for the account of the undersigned.
 
     The aggregate face amount of the Notes held by you for the account of the
undersigned is (FILL IN AMOUNT):
 
     $          of the 10 1/4% Senior Subordinated Notes due 2007
 
     With respect to the Exchange Offer, the undersigned hereby instructs you
(CHECK APPROPRIATE BOX):
 
     [ ] TO TENDER the following Notes held by you for the account of the
         undersigned (INSERT PRINCIPAL AMOUNT OF NOTES TO BE TENDERED, IF ANY):
         $
 
     [ ] NOT TO TENDER any Notes held by you for the account of the undersigned.
 
     If the undersigned instructs you to tender the Notes held by you for the
account of the undersigned, it is understood that you are authorized (a) to
make, on behalf of the undersigned (and the undersigned, by its signature below,
hereby makes to you), the representation and warranties contained in the Letter
of Transmittal that are to be made with respect to the undersigned as a
beneficial owner, including but not limited to the representations that (i) the
undersigned's principal residence is in the state of (FILL IN STATE), (ii) the
undersigned is acquiring the Exchange Notes in the ordinary course of business
of the undersigned, (iii) the undersigned is not participating, does not
participate, and has no arrangement or understanding with any person to
participate in the distribution of the Exchange Notes, (iv) the undersigned
acknowledges that any person participating in the Exchange Offer for the purpose
of distributing the Exchange Notes must comply with the registration and
prospectus delivery requirements of the Securities Act of 1933, as amended (the
"Act"), in connection with a secondary resale transaction of the Exchange Notes
acquired by such person and cannot rely on the position of the Staff of the
Securities and Exchange Commission set forth in no-action letters that are
discussed in the section of the Prospectus entitled "The Exchange Offer--Resales
of the Exchange Notes," and (v) the undersigned is not an "affiliate," as
defined in Rule 405 under the Act, of the Company; (b) to agree, on behalf of
the undersigned, as set forth in the Letter of Transmittal; and (c) to take such
other action as necessary under the Prospectus or the Letter of Transmittal to
effect the valid tender of such Notes.
 
                                        6
   2
 
- --------------------------------------------------------------------------------
 
                                   SIGN HERE
 
 Name of beneficial owner(s):
 Signature(s):
 Name (please print):
 Address:
 
 Telephone number:
 Taxpayer Identification or Social Security Number:
 Date:
- --------------------------------------------------------------------------------
 
                                        7