[1qikta]

Originally Posted by Greg Reid

Jay, he means to ground the signal side. In other words, the 12v wire that goes to the sending unit in the tank. If that is grounded, it's the same as the sending unit reading 'empty'. The gauge should go all the way left.
When you take it off ground, that is, leave it disconnected from anything, it should peg full.
If those two things happen, your gauge is good and the sending unit in the tank is probably the culprit.

Greg,

Seems like that would just blow the fuse...

[Greg Reid]

No, the gauge has enough resistance to prevent that. Remember the gauge windings are between the voltage source and the ground you're applying to the tank end of the circuit.
Basically, it's what the sending unit does at it's low fuel postion. It's just a variable resistor and when the tank is empty, the resistance is zero....Basically, a short to ground.
Second opinions welcome though! I may have forgotten something in my old age.

[Greg Reid]

PS- By the way, you can do the same check at the instrument panel but by doing it at the tank, you'll also be checking the wiring from the gauge to the tank.

[1qikta]

Originally Posted by Greg Reid

No, the gauge has enough resistance to prevent that. Remember the gauge windings are between the voltage source and the ground you're applying to the tank end of the circuit.
Basically, it's what the sending unit does at it's low fuel postion. It's just a variable resistor and when the tank is empty, the resistance is zero....Basically, a short to ground.
Second opinions welcome though! I may have forgotten something in my old age.

Thanks Greg,

OK,

I grounded the power wire in the trunk(while plugged to the sending unit). Sure enough the gauge went over to empty
as soon as I touched the body. But, if grounded unplugged without the sending unit plugged in it does not go to full...grounded or not it just lays on full.

Now what?

BTW, Is there another ground besides the tail pan ground? Maybe one under the dash?