I tried troubleshooting my fuel gauge today. It doesn't work at all.

I grounded the green/black wire. When I say grounded, that isn't EXACTLY true. I was using a test light - it has a wire with a clip and a sharp point on the other end - it looks like an ice pick, so there is some resistance there - the resistance of the light bulb. Anyhow, the needle moved up slowly. I have 12v present at the green/light green wire on the gauge.

I can't see the stabiliser, so I moved to the back of the car. There are 2 wires at the front of the fuel tank. One is a darker color. "Grounding" that with the test light causes the light to blink - maybe once or twice per second and the gauge goes up to 1/2 tank.

The other wire, which isn't hooked to anything is either yellow or light green.

Am I right to assume the sending unit is bad? Is there a way to test it?

Thanks.

likely the ground itself - most problems seem to be grounding rather than the unit

Do you have to ground the sending unit itself or just the tank? The previous owner undercoated everything and it looks like the tank isn't grounded to the frame.

try the tank - though likely the sending unit - I have to do it too and don't feel like pulling the tank

I ended up running a ground wire to the same spot I grounded the fuel pump to. It's only a short run but I wrapped the ground wire around the line going to the fuel pump and that provided support and I know the fuel pump has a good ground. That made things work after I replaced a crappy sender. Make sure you order the correct sender as sender and gauge need to match./

I fixed it!!!

I dropped the tank and removed the sending unit. I grounded the unit and moved the float up and down. No luck, so it had to be the sending unit (grounding the wire to the gauge moved the needle). Luckily I had a spare gas tank. I added a ground wire directly to the sending unit from that tank and put everything back together and it works!

I drilled a hole in the sending unit's plate, ran a bolt through it and attached the ground wire to that bolt. There is no danger in this, is there?

Thanks everybody for your help.

As long as your sending unit matches the same gauge as sending units differed in resistance. Some units showed full at low resistance and some showed full at high resistance readings. I think it all depended on how the gauge was installed or who they were getting the gauge from.

Just make sure hole is sealed. This is a ground wire after all.

It looked exactly like the old one and it showed 3/4 tank after I filled it back up, so I'll see.

I don't have the time right now with the warm weather but this winter when it gets cold and all the spridgets are battened down for the cold, I would be happy to calibrate some gauges and senders for some folks. That is the best way to do it. make sure the gauge and sender work correctly together. There is quite a bit of variability in both, plus I like to set in a reserve of about 1.5 gallons when the gauge reads empty so you can make it to the gas station without pushing. I hate gauges that read 1/4 or 1/8 when you are out. I usually fill mine on 1/4 tank now and it takes 4.5 gallons to fill it up, but I know even if its on E there is fuel in there.

Kim,

Do you have the resistance readings handy for the 3 different types of senders. I looked in my archives and could not find it.

Old type in MGAs and bugeyes 0 ohms when empty and 70 ohms when full. These work with a 12 volt power source.
newer type. 90 ohms was full and 300 or so was empty and this one uses the 10v stabilized voltage from the stabilizer.
Not sure about the 1500(rubber bumper) model gauges.
I don't know what year things changed.

Kim, the guage you reworked for Miss Agatha continues to work as it should.