Fuel level unit
 

How does the sender in each tank do its job?
I have tested the wires from the tank to the gauge and when given charge the dial moves up to full, so wiring and gauge good.
But what do the two spade connectors on the back of the tank actually do in so far as measuring the fuel level and how can I test them or repair if not operating? assume this is hard.

Normally a float on an arm , like an old toilet cistern. The movement of the arm operates a variable resistor changing the resistance to earth.

Common problem is failed floats so the arm sinks to the lowest point and never moves and neither does the gauge. Or it may try to float and you get some partial reading no matter how full the tanks are.

Hard to test without removal, to inspect the float and the rheostat (the variable resistor bit). If you do remove just be sure that the tanks are relatively empty so you dont have a petrol flood when you break the seal.

Is it running? or are you just having a break and working on something else for a bit?

Check the archive's for LnrB's recent detailed tutorial. Same sympton's in her NIX. A great illustrated tutorial, including a simple tool to remove the sender.

The unit is a rheostat operated by an arm and a float. either the float no longer floasts, or the rheostat is worn out, or both. Replacement units available. New and used.

Carl