Fuel Tank Switch Problem

[torino21]

My dad's fuel tank switch on his 95 F150 is not working. Not sure if the problem is the switch or something else. Any ideas?

[Selectron]

I assume the truck is starting and running ok, but just not switching between tanks? If so then it shouldn't be too difficult to find the problem.

The fuel pumps are fed from a 20 amp maxi fuse, then through the switched contacts of the fuel pump relay, then through the inertia fuel shut-off switch, and then the next item in the circuit is the tank selector switch. If the truck starts and runs then the circuit must be healthy up until that point.

The 12V feed into the tank selector switch (red/yellow wire) must be ok, so finding the fault would just be a matter of using a multimeter or a 12V test lamp to trace the 12V along the path from the switch output terminal on whichever pump circuit (front or rear) is not working. The problem could be in the switch, the wiring, the pump, or the ground connection.

The path for the front pump is: red wire (or brown/white wire, depending on model) from tank selector switch output to pump positive terminal, then orange wire from pump negative terminal, to a splice point where it emerges on a black wire, which connects to ground.

The path for the rear pump is: brown/white wire from tank selector switch output to pump positive terminal, then orange wire from pump negative terminal, to a splice point where it emerges on a black wire, which connects to ground.