fuel=full when headlights on?

[RWC]

I went through the technical section and didn't see anything pertaining to this particular problem (but it will be helpful when I dig into the back seat and start testing).

Before I jump in there, I was wondering if anybody had had this problem before. '89 Grand Wag: when the headlights are on, the tank reads full. When the headlights are off, the tank reads empty. Now, I haven't yet been able to verify if it will drop naturally with the headlights on, and it isn't accurate anyway (if I'm at half-tank I'm almost empty). It doesn't seem like it's following the "normal" symptoms of a busted fuel-gauge.

RWC

[talntar]

sounds like a bad ground

[Wag Rookie]

I had a similar problem, Not exactly the same but mine when the lights were off and I hit the brakes the level would drop. Coolram gave me a tip to check the tailights. Make sure you have the correct ones someone had installed 5166 bulbs instead of 5167s. In short just make sure you have the correct taillight bulbs both brake and tail.

[Brown Bear]

sounds almost like someone has routed the fuel level sending unit through the headlight or parking light wiring. Might want to check underneath truck, around gas tank region, to see if you find any PO wiring. It's easy to spot. It's usually not covered by electrical tape, certainly not soldered, and might not even have a connector on it, maybe just a notch in one wire, and fuel wire looped around it. AMHIK :D

[kyjman]

One good thing about that is if you drive with your lights on you would never run out of gas....now thats a gas.....

[Lindel]

Check the ground to the dashboard, I'll bet it's bad, or missing.