Fuel Gauge stuck

[Southpaw]

My fuel gauge was working fine, until I went to the track on Sat. I made eight 1/4mile runs with the truck, and on my way home I noticed that the fuel gauge was stuck at Full. I know for a fact it was working on the way to the track that day. Is there something I could have done to it while racing the truck?

Also - the needle isn't actually 'stuck' because when I turn the key off it drops back to empty like normal, but when I turn the truck back on it goes right back to full and stays there.

Anyone got any ideas or a fix for this??

Thanks guys

[250downunder]

Have you checked the connection to the fuel sender unit at the tank. The fuel sender unit applies 15 ohms resistance at empty and 165 ohms at full. High resistance at the connection will cause the gauge to read full. To test your gauge fit a 200 ohm variable trim pot between the sender wire and earth [disconnect the sender wire at the tank] turn the trim pot screw and the gauge should move between empty and full. A multimeter across the same connections will show what resistance the trim pot is applying.

[Southpaw]

Great info. Where exactly on the tank is the sending unit. I will probably find it, but I haven't looked yet.
Also, Electrical wiring in a vehicle is definitly not my strongpoint, what is a variable trim pot?(i've got a good idea from your explination, but where do I get one?)

Thanks again

[250downunder]

By memory there is a two wire plug in the vicinity of the fuel pump on the chassis rail; follow the wires from the tank towards the fuel pump and you will find the plug - it may be that the plug is loose or dirty. A trim pot is a tiny variable resistor. I got mine from an electronics store - I am in Australia so I can't name stores in the USA, but I think you have Tandy - try there, they are a very common component. It must be 200 ohms.