27shooter

My fuel gauge reads empty all the time. I'm looking for an answer on how to test the gauge by itself.

I disconnected the wire at the sending unit, and the needle didn't move. I believe the ground connection is good.

When the center wire is connected, I have 9.9V at the sending unit and the fuel gauge. When I disconnected the wire, I still have 9.9V at the wire. I really didn't expect to see this because I believe disconnecting the wire opens the circuit. I would have expected to see 12V at the wire. Evidently, there is a 2.1 V drop across the gauge whether the sending unit is connected or not.

I don't want to deal with the sending unit until I know what's up with the gauge.

Mr Gadgets

Shooter,
it sounds like the sending unit is open. On a car it used to be that if you ground the sending wire, it would go to full and if you open it.. the guage would read empty.. It has been a long time, but I think that is the way it works.
The sending unit is no more than a potentiometer (volume control) that changes the resistance to ground. 12v into the gauge, then the wire to the sending unit will have a voltage drop according to the resistance of the sending unit. Shorted to ground, should read full..
With the gauge hooked up.. and seeing 9.9v on the guage, check to see if you have the same voltage on the terminal at the sending unit. If not.. then the wire is open. If you do.. then tap the wire to ground and see if the gauge jumps.. if it does then the sending unit is at fault..

Hope this helps...

D*ck

stevesxm

correct in all respects

27shooter

I agree. I grounded the wire to the sending unit and the gauge didn't move.

What about my point that the gauge still reads 9.9V. I wouldn't expect a voltage drop across the gauge if no current is flowing when I disconnect the wire from the sending unit. I also read 9.9V at the sending unit when the wire is hooked up at the sending unit.

I will probably address the sending unit when the season is over. I just need technical information on how to test the gauge on the bench. I have access to power supplies and resistors.

Mr Gadgets

You are correct about the voltage drop.. 9.9 indicates current draw, but to make sure, I would disconnect the wire to the sending unit at the gauge. If the voltage goes to 12v, then there is a path to ground outside the gauge, it may not be the sending unit. If it stays at 9.9v or something other than the source voltage, then there may be an internal short. Either way.. with 12v in and either an open or short on the signal wire, the gauge needle should move, full scale..

D*ck

27shooter

I have 9.9V on the wire whether it is hooked up to the sending unit or not.