Gas gauge pegs past full when the light, brakes or park brake are on. I have had the dash out

 

doesn't sound like a gauge problem...possibly a ground problem.

 

At price of fuel today, can you do that to my car!!

Seriously, you are getting a false ground to the sending unit circuit. Check wiring at gauges.

 

While we're talking about it does anybody know where the ground from the console runs from ? There are about 5 console lamps - where does the ground for these pick up ?

 

You should have two wires at your dash fuel meter - an 18 gauge pink wire and an 18 gauge tan wire.

The pink wire is part of circuit #39 and has a common connection with the parking brake lamp, the door open warning lamp, the temperature gauge, and the seat belt warning & parking brake override relay. Circuit 39 is fed by the 10 amp gauges fuse on the fuse block.

The tan wire is circuit #30 and runs from the fuel gauge to the fuel sending unit.

At the fuel sending unit, in addition to the tan circuit #30 wire, there is a black 18 gauge (circuit #150) wire. Circuit 150 is a common ground shared with the side marker lamps, the tail/stop/directional signal lamp, the back-up lamp, and the license plate lamp.

Normal flow of electricity is from the fuse block to the fuel gauge through circuit #39, then from the fuel gauge to the tank sending unit through circuit #30, and then from the tank sending unit to ground through circuit #150.

It seems to me that normally the fuel gauge gets a constant input of power (circuit #39). The amount of power that actually flows through the gauge (fuel level indication) however is controlled by the tank sending unit.

I would first start with inspection of the common ground the fuel tank sending unit shares with the tail lights. the ground should be on the lower left frame cross member. Perhaps a poor common ground is allowing power to flow from the tail lights.

 

Common ground issues an be a PITA. I had a poor ground at the front of my car when I got it back from the body shop. Hit the horn and the headlights illuminated.

BTW, the stock sender has a resistance of 0 ohms empty, 90 ohms full. When you get a loose wire or open circuit, resistance goes to infinity and the gauge pegs over full (3 o'clock position).

 

Thanks, I think I can find the problem now with all the good information. I'll get back to it mid week and will post what I find.

 

Problem solved, weak ground.....Thanks