car

Fuel level sender in tank/ or gauge itself. You could ground sender wire at tank and see if gauge reacts/ if does sender is faulty.

To check the sending unit, measure the voltage at the tank connector. Measure the dark blue / white wire and the black / light blue wire. You'll have to back-probe the wires while the connector is still plugged in.

Hi PROTECH1980. Happy Tuesday to you. I was still typing while you were posting. This isn't the common sense circuit we're used to but the service manual isn't clear on its operation. Well, I should qualify that. According to the service manual 5.0 volts is applied on the dark blue / white wire and a varying voltage comes back on the black / light blue. If there's no voltage on the black / light blue, the sending unit would have to be open. I'm second guessing that because they use the black / light blue as a ground wire for all of the sensors and there will not be more than 0.2 volts on it. If my thinking is right, grounding the blue / white wire as you suggested will make the gauge go either full or empty. It would be good to measure the voltage on that wire first before grounding it. If there really is 5.0 volts on it, grounding it might make the gauge move to the other extreme but to be safe, use a small 12 volt light bulb to ground it. That way if it really is a 5.0 volt supply for other things nothing will be damaged by grounding it.

Hey Caradiodoc, No problem, Im glad you chimed in, Like you said the test descriptions I am looking at arent that clear. I think also if any concern about/before grounding anything you could just go ahead and ohm that sender if suspected open? / 20 ohms full-220 ohms empty. Well good tuesday to you also.