The Stovebolt Site Forums The Shop Area The Electrical Bay Fuel Gauge 46 GMC

It appears that 6v goes into my gas gauge, is 6 volts suppose to come out the other side. I'm reading 0 voltage at the wire that connects to the sending unit.

Jason,
There are 2 wires to the gas gauge.
1. Power to the gas gauge is received from the switched side of the ignition switch which means the gauge only works when the key is on.
2. Another wire goes from the other terminal on the gas gauge to the sending unit. This wire does not have voltage on it. It reads Resistance from the sending unit which is determined by the float in the tank. This resistance makes the needle move.
Check this article out.
http://www.chevytrucks.org/tech/gasgauge.htm
Harold

The sending unit varies the ground or negative to the gauge hence moving the needle. You need to ground your sending unit and using a volt meter measure the ohms as the float goes from empty to full. If I'm not mistaken you should see more resistance when at full creating more ground to the gauge, less resistance/ground shows empty on gauge. To test your gauge simply ground the terminal opposite the positve and it should go to full. Could be a bad coil in the gauge or a bad sending unit. Hope this helps.

Aah Harold beat me too it.

Harold46 and Gmans 45,

Quick question: If you ground the terminal that goes to the sending unit, will you short out or burn out the gage itself? I would hope that Chevy built the gage to handle periodic grounding, but how much full current can the gage stand?

Thanks,

Bill

Bill, you don't ground the terminal that goes to the sending unit. You ground one of the 6 screws that attach the sending unit to the tank.

You can unhook the wire going to the sending unit and ground the wire only, to test the gauge. This doesnt hurt the gauge but instead acts as a full on ground meaning the tank will either show completly full or empty, I can't remember which.

Jeff

Hi Jeff,

I tried grounding as you suggest. The gage installed in the truck and the spare both "jump" just above E and stop. At this point, I'm certain that the gages are both shot/shorted. I'm going to disassemble and try a repair. Otherwise, I'll install new a new gage.

Thanks for the clarification.

Bill

No, a gauge that pegs to full might be fine. That behavior could be a result of a broken lead somewhere in the gauge circuit.

Here are some causes/remedies that are described in Shop Manuals.

Disconnect the lead from the gauge to the sender - a good gauge will peg Full. Then, run a lead from the sender post on the gauge to a good ground - a good gauge will read Empty.

After that, test the sender unit (outside the tank). These are simple to "bench test".