I’m debugging a gas gauge issue on a 67 camaro and could use some guidance. The gauge continues to show a level after the ignition is turned off and assume it should show empty. Can anyone confirm if that’s correct? I’ve done typical testing of the sending unit by disconnecting the positive lead (simulating full) and shorting it (simulating empty) but neither happens. I suspect the wiring from the sending unit to the gauge is bad or the gauge itself. Anyone have any thoughts or further debugging techniques? Also, I found the positive wire to the sending unit remains hot with the key off. Shouldn’t it be wired to a switched power source and only be hot with the key on?

Thanks,
Steve

 

I have not dug into this, but I do believe the power to the sending unit should turn off with the key. This a very simple circuit. Think of the in tank unit as a volume switch. You put power to it the more you turn it the power level goes up/down. The gage is just reading the power level coming from the volume switch. Note this is a generic description it could just as easily be that the sending unit supplies the ground.

A quick look at a schematic will tell you what it should be. I am at work so I can not look it up. I suspect at some point the gas gage stopped working because it lost power and someone just ran a full time power supply to get it working. If you used a battery maintainer you would never know. Moving the wire to the key on side of the fuse box should not be difficult. You just want to be 100% sure there is a fuse. Last thing you want is to burn down your rig. Any wire with power needs a fuse. Schematic should say what fuse the power should be pulling from.

 

I had issues with a after market fuel gauge for my Camaro and here is what I was told to do.
First, your fuel gauge should not a constant 12v, if it does that needs to be fixed.
The gauge should have a power supply, ground and a post for the sending unit. The sending unit is just two posts, signal and ground.
To check your sending unit, take the signal wire and ground wire off, take a volt meter and and touch the posts, if you have no fuel, it should read 0 ohms, or say a 1/4 tank, it should be around 22.5 ohms, full would be 90ohms. If things are good, hook the wires back up, then check at the harness where it plugs into the gauge, you should get a similar number. If not, your signal wire could be damaged.
I have a friend that works at Autometer that helped me out and there is a way to check if your gauge is good, but I forget and if you would want, I could get in touch with him for the instructions.

 

Thanks for the help guys. Seems we all agree I should have constant power to the sending unit. I'll get that fixed.

Bruce, I'll run those tests and if it all checks out except for the gauge I might take you up on getting some instructions from your friend.

Thanks again,
Steve

 

Open trunk and find a brown wire drive side of latch structure on floor as this wire goes to sending unit. Use ohmmeter and measure referenced to body ground. Siphon gas out and see indication.
0 = empty; 90 = full

You can also insert a 50 ohm resistor between pulled wire and ground screw in seeing the gauge indication. Approximately half tank.
Needle is on its own with key off. As long as it indicates with power on, who cares.
There is the sending unit return wire in front of tank and you might remove and wire brush both terminal and floor, smear grease on both and reattach.