Where is the fuel pump relay located on a 1988 GMC Sierra? The fuel pump relay on a 92 gmc 1500 is located on the passenger side of the firewall behind a black plastic cover. The fuel pump relay on a 1988 Mercury Tracer is located to the rear of the 1988 GMC 1500 fuel pump relay location - Fixya 1988 GMC 1500 fuel pump relay location - Cars & Trucks. Posted by Anonymous on Jan 07, 2012. How do I jump a fuel pump relay of a 1988 GMC K2500 with a 5 to get power to a sending unit from a 1998 GMC C1500 with a 5 V8? Not sure that we are thinking of the same thing. The wires to the gas tank operate the fuel pump and the fuel gauge.