[LovinMyBird]

I have an 1985 Trans Am and about a month ago the gas gauge quit working on me and all it would read is full and not move. Yesterday when I ran into town the entire trip my gas gauge was going crazy, going from full to empty and back so many times that I couldn't count. What's wrong with it?

[da34guy]

Sounds like ya lost the ground.

[CustomConspiracy]

I have a 65 C-10 pick-up. The gage was working fine.
I removed the gas tank from inside the cab, and let it set empty for a couple of months while I worked on the truck.
When I installed the tank in the bed of the truck, the gage did kinda the same thing. Read full all the time.
I checked all the wires, several times.....no fix.
When I removed the gage float and sending unit it turned out that the little flat strap of metal that is used in place of wire inside the tank, had cracked where it was riveted to the mount.
I tried like crazy to solder this thing but it would not work.
Eventually I managed to bend it just right, so it makes contact just thru being in a bind.
If I keep the current tank and location, I will spring for a new gage. I may switch over to some S10 tanks and electric pump, and use the gage that comes in that.
In your case if you can,t find the short on the outside, maybe the gas sloshing inside is causing the thing to periodically break contact.

[LovinMyBird]

Any ideas on where this loose ground would be?

[CustomConspiracy]

On mine, the only ground is from the sending unit to the body. The rest is mounted on rubber.
It's just a short wire running from the top of the sending unit to a goo ground point.
The power wire, which on mine runs to a special 5v terminal on the fuse block.
I guess the signal to the actual gage goes from the fuse block to the gage?
I checked everything and could NOT find a short, so if you do that too, and can't find the problem....look inside the tank at the sending unit and see if it did what mine did.

[curtis73]

almost always you can count on this... a guage that reads empty means the sending unit/guage isn't getting power. A guage that reads full means the sending unit isn't grounded.

I had a similar problem. My gauge read full except when it was raining