On many GM applications, the wiring harness that connects to the fuel pump assembly is not properly inspected as part of fuel system repair. This harness is prone to failure, leading to misdiagnosis and vehicle come-backs. Connector housing cracks, pin and contact looseness, and wire crimp issues can cause symptoms that simulate an issue with the fuel pump. It is recommended that the wiring connector be replaced with the pump to avoid unnecessary problems.
*Tech Note: When replacing the fuel pump harness connector be sure to remove as much of the old wiring as possible. For example, if the connector had a poor connection this would create a resistance problem resulting in heat. This excessive heat melts the wiring insulation allowing moisture to enter and corrode the wiring, resulting in future problems.
How to identify the fuel pump wiring harness connector on 1999-2003 Chevrolet Silverado and GMC Sierra trucks: first look at the new pig-tail connector. You can separate these four wires into two circuits by the gauge (diameter or thickness) of the wire; two wires will be bigger gauge than the other two. The thicker gauge wires are for the pump to handle the higher voltage drawl. The smaller gauge wires are for the level sensor, a low voltage circuit.
Wiring color does vary from model to model, but with noting the wire diameter this is easy to work through. Working with the larger two diameter wires first, the black wire (pump ground) will match to another large diameter black wire. The 12 volt pump feed wire will be most-likely gray but it is not unusual to see a white wire here (just be sure of the gauge diameter).
Now working with the two smaller gauge wires for the fuel level sensor. The level sensor signal wire is purple and sometimes with a white tracer stripe; this will match up with the connector purple wire. For the level sensor reference wire, the orange/black wire (on the supplied connector) will connect to the smaller black wire on the vehicle harness. *NOTE: On very early models this small black ground wire may not there. No problem, just connect this wire to the other ground (the large diameter black wire).
