Does anyone have a schematic that shows the fuel tank sending units and dual tank solenoid for an '86 F350 with a carbureted 460? It is a Canadian built truck if that makes any difference. I can't either tank to register fuel on the gauge.

 

The yellow/white wire comes from the gauge and enters the motorized fuel selector valve on the frame. This valve has contacts in it that switch the sending unit wires.

 

Thanks, now maybe I can get this thing figured out.

 

Well, got it traced all the way to the firewall plug below the master cylinder. Grounded it there and gauge is still not moving. I can see where the yellow and white wire goes from the gauge cluster into a pink wire loom that splits behind the heater control and then goes up. I'm guessing it goes over the top of the instrument cluster then down around the e-brake into the main harness and back out the firewall? Not much room for an old fat boy trying to stand on his head and follow the wire from there.

I guess it could be the gauge itself but all the other gauges are working well including the factory tach.

 

So you found the yellow/white fuel gauge wire under the dash, and with the key in run, grounded this wire and then ungrounded it, and the gauge didn't move? Were you able to disconnect this wire? The ground/unground test is not going to work if the wire is grounded all the time by a problem somewhere.

You have tried the ground/unground test back at the valve on the frame already correct?

You can also put a meter on this wire from the gauge, and with the key in run, you should get a blinking voltage on the wire. The blinking voltage is the gauge regulator feeding voltage to the gauge.

 

I grounded the Y/W wire at the valve on the frame, with the key on and the gauge never moved. I also unplugged the 4 pin connector on the engine side of the firewall and grounded the Y/W wire right before it goes into the firewall, again with the key on, the gauge never flinched. I'll check for blinking voltage at the 4 pin connector and verify Y/W wire continuity from instrument cluster to the same 4 pin connector next.