I may have teh schematic...if I find it I'll post what I find, but if memory serves...you ahve a blue/yellow wire which is the wire for your front fuel gauge, a brown white which powers the gauges on teh dashboard, and 2 wires, control the selector valve. It works by reversing polarity to pin 1&2 on the harness. The back tank gauge sender wire is yellow/light blue, and if you poke around underneath the truck, you'll find that the first two wires I can't remember if its the outside 2 or inside 2 but when you plug in your voltmeter it will be the one that has +12V key on in the front tank position and -12V in the rear tank...or I may have that backwards, but either way, the 2 wires will have 12V at all times when the key is hot, the polarity controls which tank is used. In all likelihood the selector valve quit working or teh rear tank rusted out and the Po wanted to deep six it and keep driving till he could dump the truck. A new selector valve is $90.00 and a new tank is about $120 for stocl steel or a lot more for a plastic or oversized tank. You could also try contacting ARGVE, he taught me everything I know about this system and still knows it very well even though he went over to the dodge side.
J.D.
Hello im new here my name is ray, i was comming in to ask if anyone knows what color the sending unit wire is from the front tank of a 6.9 86 diesel as somone has hacked mine to bitz and i would like to see if my gauge works..also what color is the wire to the gas selector switch for the gauge. they threw the rear tank in the trash so i got a selector with only one tank and its a front tank...
