fuel sender unit

[DeputyMike]

can anyone tell me how to tell if my fuel sender unit is bad, the wiring is bad, or if my fuel gauge is bad?

[yipster]

took my loose contact out not so long ago without burning myself

[TerryKing]

Most fuel senders have a variable resistance. Here's something from "HowStuffWorks": http://auto.howstuffworks.com/fuel-gauge.htm

When the float is near the top of the tank, the wiper on the variable resistor rests close to the grounded (negative) side, which means that the resistance is small and a relatively large amount of current passes through the sending unit back to the fuel gauge. As the level in the tank drops, the float sinks, the wiper moves, the resistance increases and the amount of current sent back to the gauge decreases.
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Bottom line: connecting the wire that usually goes to the fuel sender to GROUND will normally give you a "FULL" indication. Disconnecting the wire completely will normally give an "EMPTY" or below-empty indication. If your display gauge acts that way, it probably is OK. If it does not, the sender is suspect. And if you suspect the wiring, then disconnect it at the gauge, and test with OPEN and GROUND to the gauge.

Unfortunately, the in-between values are "It Depends" . It depends on the particular fuel sender-gauge combination. IF you can find a direct replacement sender, you can measure the resistance VS movement with a multimeter. You COULD get fixed resistors of the correct value for some of the in-between values to test the gauge with. Or connect an out-of-the-tank sender, to your gauge, move it to different positions, and see the gauge readings... A Typical (Probably not yours!) reading at "Empty" may be between 100 and 250 ohms, and something like 20 ohms at "Full".

Post the details, and someone here MAY know the resistance values for your sender....