fuel sending unit / fuel gauge mystery

[airbornewally]

OK, so I've recently inherited a 1972 C10. My father-in-law has used a stick for as long as I can remember to measure the amount of fuel in the tank. I have read many threads regarding this problem (not necessarily using a stick, lol), but haven't really been able to find a solution yet. With the sending unit installed in the gas tank, and the wire attached to the sending unit the gas gauge reads 'empty'. If I remove the wire, the gas gauge spikes past 'full'. However, if I remove the sending unit from the gas tank, attach the wire and ground the unit, the gas gauge works! I have ohmed out the sending unit. I know it's supposed to read between 0-90 ohms, respectively representing empty thru full. The reading I got on the sending unit was closer to 15-105 ohms. I have made sure that there are no cracks or pinholes in the float. It just seems to not work when the darn thing is installed in the gas tank! I know I must be missing something. If anyone has any ideas, I would be greatly appreciative.

[cdowns]

have you tried running a good ground wire directly from the sending ynit to the body of your cab?

[fixit-p]

You've done all the tests now you just need to interpret your results. I see 2 possibilities 1, your float is stuck (down when in tank) or 2, when installed in tank your sender wire is shorted to ground (check the insulator or if terminal is making contact with tank). When the sender is installed in the tank is the empty reading on the gauge (float down) the same as when you tested it out of tank and grounded? If the reading on the gauge out of the tank was slightly higher than when it was installed it would point to possibility #2 above.

[airbornewally]

I will definitely check out the insulation on that sending unit wire and update if I get any new results, thanks!

[cheguevara]

Did you get the sending unit fixed? Was it the ground wire?..I got the same issue
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