Fuel gauge

[jogadaman]

I have a 63 Riviera, and the fuel gage does not work. It shows full all of the time. Is there a simple way I can tell if it is in the gage or the tank sending unit. If the wires to the gage are disconnected, should the gauge read empty? I have a write up on how to check if it is in the gage or tank sending unit, but it calls for a good sending unit to be used to check. Since I don't have a spare sending unit, is there another way? Thank you.

[62BuickFan]

This is a good one. These guages work off of resistance. The part in the tank has a variable resister, and as the float goes up and down, the resister sends a different amount to the guage. Usually in the form of ground. So, to answer one of your questions, I would ask you one first. Does the needle go to E when you turn off the key. If it does, then probably the sending unit in the tank is bad. Because, the dash part of the guage is getting power and responding to it. It is also getting a full ground which would indicate that the resister is bad, and not producing resistence.

So, I would check your tank sending unit first and go from there. That is not the simple way, but one way or another you are going to have to take something apart. Just run it really low on gas and drop the tank. You might find that the wire is unhooked or has a cut in it. If that is the case than case solved. I would get an OHM meter and check the wire by itself and the sending unit. Then you will know.
Good Luck.

[the skylark]

Disconnect sending unit wire from tank, or along wiring harness close to tank, Observe gauge. Ground sending unit wire. Observe gauge. If no change, gauge or associated wiring is fault. If readings are opposite, sending unit or tank ground is faulty.

[the skylark]

Oops! forgot to remind you to turn ignition on while observing gauge. I know that sounds like a "no brainer", but sometimes the simplest things......

[jogadaman]

The fuel gauge does not move when I turn the key on or off. It stays on full all the time. Is the gauge suppose to go to empty when the key is turned off? From what I am hearing from the response so fay, it sounds like the problem is in the gauge. I did unplug the sending unit wire which is located to the right of the gas fill under the back bumper. When i disconnected the wires, the gauge remained on full.

[CyberGolem]

This is a really old thread and you may have already figured out your problem --and if you have please post what you did to fix it. I'll post anyway in the event others are still having similar issues:

It sounds to me that the gauge is receiving maximum resistance in the circuit, which is why it's reading FULL. If you simply disconnect the lead wire in the trunk (mine is yellow) and connect it to the ground/ body, the needle should go to EMPTY since the circuit should no longer have any resistance.

Also, disconnecting the wires should cause the needle to fly past the FULL mark and peg.

Being a balanced-type pointer, the needle should come to rest on either side of the gauge when the ignition is turned off (gravity). Since yours doesn't then you must be getting some juice to the circuit somehow. I've heard this may due to the dimmer switch... ?? Could be since my schematic shows a yellow wire connected to the dimmer as well. I'm checking into that today to see if there's a correlation.

Cheers,
-Chaz