FUEL GUAGE


Q:

I have a problem with my 1961 Corvette that I have never been able to repair. The gasoline gauge needle jumps up and down whenever I use the brakes or the turn signals. If I keep my foot off of the brakes, and don’t use the turn signals, the gasoline gauge works perfectly. The gauge itself reads accurately, until I use the brakes or turn signals.


I have tried new light bulbs, a new brake light switch, and even a new gasoline gauge tank device, but, I keep having the same problem. I know it didn’t work that way when the car was new, so why does it persist that way now? How can I repair this?


A:

The problem you are having with your Corvette is quite common. The good news is that it can be fixed.


Essentially, an improper ground in the rear lamp circuit of the car causes the problem. You asked why it does it now; after all, it worked properly when the car was new? That is a good question. The answer is that, when the car was new, all the electrical devices, including the wiring, switches, lamps, sockets and grounds were new, and not corroded or oxidized from time and environmental causes. Because these parts were new, the grounds were adequate, and the circuits worked correctly. As time went by, normal aging of the parts, and chemicals in the environment have caused the formation of tiny amounts of corrosion, and thus, a reduction in the flow of electrons in the circuit. Also, in time, crimped parts, like those in the sockets and lamp housings will loosen, causing a bit more resistance to electric current flow. This is because the electrons must flow through the bulb, bulb socket, socket to inner housing, inner light housing to outer housing, and finally to the ground wire.


The aging I mention would not be as much of a problem if there was a ground location at the rear portion of the car, but, the only ground for that entire circuit is located up front at the engine itself. As a matter of fact, an interesting observation I have made is that, if you look at the wiring diagram of the 1958-1960 Corvette, you will see that the engineers placed a ground wire at the rear of the car. It attached to the rear bumper bracket, and helped to ground all the electrical parts nearby. When they designed the wiring harness for the 1961-1962 Corvette, they did two things that, I believe, ultimately caused this problem: they doubled the number of tail lamps, which doubled the current flow, and they left off the rear ground wire altogether.

I have used several methods to repair this problem, but the simplest one I have found is to attach an additional ground wire to the gasoline gauge sending unit, located on top of the gasoline tank, and to attach the other end of the wire to a good ground location on the frame of the car. On the tank sending unit, I like to strip the insulation off of the wire, splay the ends of the multi strands like a broom, and, using a soldering iron (NO FLAME) solder the broom like splayed wires to the flat surface of the sender itself. This makes the best connection. Alternatively, you could clamp the bare end of your new ground wire to the pipe nipple on the sending unit, using a small hose clamp.


The most common way to connect the wire would be to use a wire terminal on the end of the wire, and attach it to one of the screws that hold the sending unit to the tank. I don’t like to use this method because, each screw has a small rubber “O” ring around it to help seal gasoline fumes, and I fear that the ground terminal will possibly interfere with the sealing of the screw. After attaching the ground wire securely to the tank end, pass the wire down through the body of the car, where the fuel line goes, you will be able to route it to the right side  exhaust hanger, near the frame cross member. I place a suitable terminal on the end of the wire, and, using a star washer for better electrical contact, attach it to one of the cap screws that are used to hold the exhaust support.


Adding a ground wire in this location is not as noticeable as adding additional grounds to the tail lights in the trunk. It is simpler also, because you only have to add one wire instead of four. Actually however, if you add a ground wire anywhere in the rear harness, it will probably help alleviate the problem.

At the same time you add this ground, check the other connections in the electrical system for looseness, corrosion or dirt. Clean the connections at the battery. Check the generator belt tension as well.


I hope this helps with your gasoline gauge problem.