Hello all. Maybe you might be able to help a newbie like me

I have a 71 with a new fuel tank and sender, a new oil pressure switch and a new temperature sensor. When I turn the car on, the red idiot lights all light up as they should, but never turn off and the fuel needle pins way past full. I figured the gauge is bad. I bought a used one and the exact same thing happens.

I know the little bolts that hold the gauge in place are the ground, so I know it's grounded correctly.

Do you think the harmonica connector might be bad? That seems really unlikely.

Any obvious ideas???

Thanks everyone.

 

Your fuel gauge pinning way past F indicates an open circuit in the fuel gauge wiring. Your gauge should go to E when grounded (zero resistance) and way past F when open circuit (infinite resistance). You can disconnect the gauge wire coming from the gas tank in the rear license plate area and then connect the side coming from the gauge directly to ground. With the key ON, the gauge should go to E. Pulling the connector apart with the key ON should cause the same thing as you're seeing now, the gauge going way past F.

If the gauge responds this way, there is nothing wrong with it, which suggests looking elsewhere. Are you sure the ground side of the sending unit was connected? If not, the circuit would always be open, and you would see what you're seeing. You need to get down under the car and see if the ground wire is properly connected to the car's frame. You don't say what kind of '71 you have (Cutlass? full-size?), but on my '67 Delta 88, the ground wire comes forward from the top of the tank and attaches to a screw in the frame right there. This area gets corroded and crud-covered over time, and it's easy for the ground to fail after enough time even if it is properly connected. I would assume that, since you had a new tank installed with a new sending unit, the area around where the ground wire would be connected would be cleaned off to bare metal. But the only way to know for sure is to put the rear of the car on jack stands and crawl underneath and take a look.


The problem with your idiot lights seems to be the opposite. They light up in actual use when whatever switch they're attached to closes and completes the circuit. In other words, in normal operation, you should be able to pull the wire off of the oil or temperature sending unit, touch it to the engine, thus grounding it, and have the idiot light go on. The fact that all your idiot lights stay on suggests a ground somewhere where there shouldn't be, and the fact that ALL of the idiot lights stay on suggests a problem with the connector as it is unlikely that all the sending units are bad at the same time.