Fuel gauge wire.
 

I have a 79 k10 with dual tanks , today my fuel gauge started reading way past full no matter with tank was turned on. I removed the gauge and stuck a jumper wire to the plug from the back of the tank selector switch and the gauge would then read each tank correctly because I know the levels. So I was assuming the switch went bad but when I switch it from left to right I hear the solenoid underneath making a noise as if it where working . Does anyone know the path this wire takes so I can track it down.

Re: Fuel gauge wire.
 

If you are able to get a correct reading on both tanks using a jumper wire in place of the selector switch, then it sounds like your original diagnosis of a bad switch is correct.

The selector switch has 2 sets of contacts inside. One set switches the gauge between the sending units while the other set of contacts operates the solenoid valve. So that would explain why your solenoid valve is still working okay.

As far as the wiring goes, the switch takes the tan wire from the gauge and switches it between either the tan/white or blue wire for the sending units. And it also takes the pink/black +12V feed from the fuse panel and connects it to the light green wire to power the solenoid and select the auxiliary tank. It leaves the green wire un-powered to select the production tank.

Re: Fuel gauge wire.
 

good luck I have been trying to get my 77 k3500 fuel gauge working and still haven't figured it out it has one pink and blk hot wire running from fuse box to switch its has five poles I cant figured where to look I have done pulled out the dash pad cluster its a tan white wire it run from the dash switch which only has 4 wires to it to the Pollack switching valve I am running with new tanks and sending units with electric fuel pumps I have 6.0 in my truck

Re: Fuel gauge wire.
 

I want to say (but I'm not 100% certain) that the electrical connections for fuel sending units and the solenoid are on their own connector through the firewall, but near the fuse block and other connectors on the driver's side.. The wires then get routed up and across the firewall, and routed down the passenger side frame rail.

I have the same setup, I worked on it a few years back, dropping the passenger tank and replacing the sending unit, so I think I'm correct, but I'm not positive. I remember the basic circuit, but not the fine details.

I could get you pictures from my truck, but it would probably take a couple days...

Re: Fuel gauge wire.
 

i dont know if it helps but on the 80s truck the fuel gauge wire dropped out of the bottom of the fuse box under the hood and went down the frame so it was easy to find. but i believe this one is pink in color