["QUICK-SILVER"]

Originally Posted by Greg Reid

What you're describing is kind of stramge. You ground the wire while the circuit is complete and it goes empty but you ground it with the wire unhooked from the sending unit and it stays full?
I'm thinking it should have gone to empty either way.

Unless the guage IS bad, but then the first empty reading wouldn't have happened.
Unless another possibility, a broken wire in the ribbon running from front to back and wiggiling the harness/connector had it making and breaking contact. But it doesn't really sound like it though.

Think of the fuel guage as an ohm meter, thats only capable of reading 0/zero (dead ground) to 90 ohms. And 0 to 90 is all the sending unit can produce. 0=empty and
90=full.
With the connector unplugged, on the back/trunk side, you can test the sending unit with an ohm meter. Sending unit wire to ground should read 0 to 90 ohms if it's good.

You can perform the same test on the spare sending unit and move the float up and down to see the 0 to 90, if it's good. If it is, hook it to the car harness and see if the fuel guage works.