Ever since I bought my 92 Bird, the fuel gauge has not moved. It's stuck about 3 quarters of the way full and does not budge when it's on or off. I can't find any infomation in my repair manual (probably not looking in the right place), but I'm curious as to what kinda problem I'm looking at. I know I'm going to have to drop the tank, but any tips, walkthroughs or suggestions would be very helpful. Thank you!

 

The fuel gauge is a pretty simple system. 12 volts is supplied to one side of the gauge. The other side goes to the sending unit in the tank, which has a variable resistance depending upon fuel level, to ground. As resistance varies, the voltage through the gauge varies, which is what moves the needle on the gauge. (I forget off the top of my head which is empty and which is full - I believe 0 ohms is empty and 90 ohms is full, but it may be the other way around.)

In order for the sending unit to be the cause, it has to be keeping the resistance the same regardless of fuel level. The only ways it can do this is if the float is stuck (not likely), or the variable resistor is staying at the same resistance due to some internal fault (not likely). The easiest way to check that would be to disconnect the harness back by the tank, turn on the ignition, and see if the gauge moves - if it does, then the fault is in the circuit you disconnected. If it doesn't, the fault is in the gauge, or the circuit between the gauge and where you disconnected it.

By the way, the gauge may not move when you turn off the switch in a properly operating system. Doesn't with my '86 instrument cluster.