On and off Gas gauge

[Lynx]

My gas gauge has been acting weird lately. It works some times... When it is working it reads fine and then all of a sudden it will just start droping and sit at empty. It used to work but just recently it started acting up. I have dual tanks as well but they have never worked since I have owned the truck. Info below VVVV Any ideas on whats going on? Im assuming its wiring but not sure where to start looking.

[Lynx]

Hrmm so now i checked the grounds down by the tank, Lossened them and then tightened them up again and now the darn gauge pegs way past full.... God love 21 year old butchered wiring...

[NeCrOmAnCeR]

Sounds like you have some bad wiring. Check for continuity on all ground wires and the wire which goes up to the guage.

[nn2004]

Man I have this problem on my 87 too. My truck had dual tanks at one time, but does not longer. They disconnected everything. When I plug the main switching valve under the truck back in and poke a test light into the pink wire for the gauge, it reads 1/4 or less, and I have a little under full supposably. If you fix yours man let me know. It is driving me crazy. Especially since this wiring diagram I have is half butted and doesnt show half of the stuff that it's supposed to. If I find a solution to mine, I'll let you know also. Good luck.

[Lynx]

Yeah for sure, im going to check out my wiring diagrams again and then get under there and make sure the grounds are good and then start testing.

[nn2004]

Well, I eliminated a few things on mine. Yours may be a bad gauge. Supposably, when you ground the wire going to the gauge, it will read empty, which mine does. When everything is disconnected, it should read past full. I finally figured out all the wiring under there and got the right wires hooked up. Since my left tank is no longer there, I hooked the pink (gauge) wire to the pink w/black wire (right sending unit), and I get a reading of 3/8. Gauge appears fine. I was told it ALSO can be the ground on top of the tank. Since there is a rubber o-ring in between the sending unit plate and the tank, the ground must be connected with a wire that goes to the frame, and supposably a spade terminal is on top of the unit for it to connect into. I wonder if you have to drop the tank to get to that spade terminal.. A way to check it without much work is supposably to get a reading with an ohm meter between the frame and the tank. The reading should be less than 1 ohm since there is rubber insulation between the tank and the frame. Just some info I obtained that I felt I should pass on..