My fuel pump has been bypassed with an on and off switch. all the wires for my 1991 mustang GT are still there it just won't turn the pump by the key. it works fine when i turn the switch on but not by the key. I have checked the relay under the drivers seat but it didn't change anything. In am wondering what else could be keeping the fuel pump from coming by the key. i dont know if there is another relay because all my fuses are fine and the relay under the driver seat. So please help me figuer out this problem. please
fuel pump on 1991 Ford Mustang GT
by beverly secrest in Rocky Point, NC on May 10, 2010
ANSWER by Splitshaft , November 17, 2015
The EEC IV engine control module powers the fuel pump relay pull-in coil through the inertia switch at the rear of the car. An open inertia switch or failed EEC IV computer can result in an inoperative fuel pump relay. Electric power for the fuel pump is supplied through a fuse link at the starter motor relay on the inner fender. The electric power for the fuel pump flows though the fuel pump relay contacts when closed by the EEC IV computer. Eliminating the bypass switch and restoring normal fuel pump operation will impart significantly greater safety.