Automobiles today are better than ever before. The cheapest little economy car today is a far better car than the early straight axle Corvette ever was. I didn’t say it was as much fun or exciting as our Corvettes, but, as a practical matter, it is a much better car. This is not because the GM engineers of the fifties didn’t care to do a good job, or that they cut too many corners, it’s because the technology of today is superior to what was available at that time. And new materials and technology enable car companies to build a better product, for less cost. It is also true in the 30 to 40 years that have transpired, some of the repairs made to old Corvettes have not been what they should have been. For whatever reason, I find the same problems over and over again in these early cars. One example is the “Dancing Gasoline Gauge.”

This problem is one a lot of you are going to recognize. It affects Corvettes from 1958 through 1962. The gasoline gauge needle will jump to the right whenever you turn on the headlights, put your foot on the brake pedal, or, as the turn signal is operating, the needle will dance in a movement back and forth with each flash of the turn signal lights.

I receive many phone calls and letters from people frustrated after having spent time and money trying to solve this problem. New gas gauges and tank mounted sending units are often installed in an effort to repair the trouble, to no avail. Most have given up, and just learn to live with it.

Good news! The problem can be solved. The cause is usually located in the ground circuit serving the rear lights and the fuel tank sending unit of the car. In a few words, there are poor grounds in this circuit. The result of these poor grounds is that the balance in the fuel gauge is interrupted each time you operate anything in the circuit.  That is, each time a light is turned on or off, the balance that exists in the fuel gauge is electrically changed, causing the needle to move. If the ground path for each of the electrical components were adequate, the operation of the rear lights would not affect this balance, and the needle wouldn’t dance.

To understand the problem, we will have to look closely at these electrical grounds. It’s clear to me the design of the circuit is partly to blame and therefore, many cars are affected. I will try to explain...

The Corvette body is made of fiberglass instead of steel used in so many other cars. This is part of the problem because the fiberglass body is not a conductor of electricity. In conventional steel bodied cars, the body itself is used as the ground path for most electrical components. In the Corvette, it is necessary for an individual ground path to be provided for each electrical component. Therefore, you’ll find there is a separate ground wire hooked to each light, and to each horn, and to each of the various housings such as instrument cluster, heater/clock console, radio, windshield wiper motor, etc. These ground wires are all hooked up in common. Within the electrical wire harness, there are several junctions where groups of ground wires are all soldered together. The ground wire circuit travels all over the car. It can be checked and traced with the help of the wiring diagrams found in the 1953 - 1962 Corvette Servicing Guide (ST-12) and in the Assembly Instruction Manual (AIM). Ultimately, they all end up at the negative terminal of the battery.

The ground wire is every bit as important as any other wire in the circuit. In order for any electrical device in the car to work, it must have an adequate path for the current to return to the battery. If this path is not maintained, the device will not operate. In the case of the fuel gauge, the devices are working, but there is too much resistance in the ground circuit and the operation of the gas gauge is being affected. It is being affected because the gauge is a delicate instrument with a needle balanced between two electromagnetic coils. These coils of very fine wire are located within the fuel gauge unit in the instrument panel. The gauge unit in the fuel tank is a variable resistor, which changes its value as the level of fuel in the tank changes. As this happens, the current in the two coils change in relation to one another, and the reading of the gauge varies. It is designed to relate directly to the level of the fuel in the tank.

The problem starts when the ground circuit for the gauge, which is shared with the tail lamp, stop lamp, and license plate lamp circuits, develops too much resistance for any reason. This extra resistance changes the balance between the two coils, and therefore changes the reading on the gauge. Let me illustrate how this problem has happened...

If you look at Photo #1 (above), which is a front parking/turn signal lamp for a 1958-62 Corvette, you will notice it has three wires coming out. One is for the parking light filament, one is for the turn signal, and the third is the ground wire. This lamp has its own built-in ground wire.

The wiring harness has a companion wire. When hooked together they provide an excellent ground path. The headlamps also have built-in ground wires.

If you inspect the tail lamp unit you will find it does not have a built-in ground wire. The wiring harness has the ground wire, and it’s designed to be fastened to the mounting post of the lamp housing when installed. A terminal on the end of the ground wire fits under the hold down nut, and the nut is intended to provide the connection for the ground. This is one of the problem areas in the rear lamp circuit, but it is not the only problem.  If you look closely at the design of the rear lamp assembly in Photo #2 (on next page), you’ll see it’s made out of several parts, all crimped or riveted together.  Please note I have soldered an extra wire to the outside of the lamp socket. GM did not design that wire!

In order to understand the ground path completely you have to look closely. The electrical current, after passing through the filament, must then pass out of the base of the bulb to the inner socket (the one I soldered the wire to), then to the outer socket (marked B), then to the inner housing (marked C), then to the outer housing (marked D), then to the ground wire terminal, and then to the ground wire (not shown). When I said we had too much resistance, this is what I meant. Each connection adds resistance to the circuit. Age adds resistance to the circuit. This is why I solder a wire to the inner socket. In this way, I jump over all that extra resistance. I attach this wire to the ground wire by removing the terminal of the ground wire, and installing this extra wire, along with the regular ground wire in a new terminal, which I install over the mounting stud in the usual manner.

I do this for each rear light and sometimes do it for the license light(s) as well.

I know the engineers designed the lamp to operate without this extra wire. They specified (continued on next page) the pieces would be attached to one another in such a way that there would be very little resistance between each part. But even if there is no excessive resistance between the parts, the ground wire, which is designed to be connected over the lamp mounting post and secured by means of the simple self threading hat-type nut, is a poor ground. By soldering the wire directly to the inner socket, the ground path is made near perfect. If, however, you don’t care to solder the extra wire because of changes in the originality of the parts, may I suggest another possible repair method?

In Photo #3 (right, above), you’ll see examples of star/tooth washers. These are available in internal or external-tooth types, as shown, or another type, which has teeth on both inside and outside diameters. These washers will cut into the metal as you tighten the nut against them, and the cutting action will provide an excellent electrical connection.

If you place one of these washers under the terminal of the ground wire, or between the terminal and the mounting nut to insure a better ground connection, you may reduce or eliminate the “Dancing Gasoline Gauge”.

Another problem area is the connection between the ground wire and the gas tank-sending unit. I have drawn an illustration (at right) of the small screw used to attach the ground wire to the sending unit at the tank. It is one of five screws, which secure the sending unit to the tank. if you will notice, there is another sealing washer under the head of the screw. This is necessary to keep gasoline from seeping out and causing the inside of the car to smell of raw gasoline. Note the placement of the cork gasket, rubber sealing washer and ground wire in relation to the fuel gauge unit.  The connection between the ground wire and the fuel gauge unit is the point of interest.

You could place a toothed washer between these two parts, and it would help insure a good ground, but it would interfere with sealing of the gasoline fumes. Instead, I would recommend soldering a wire to the sending unit as shown in Photo #4 (opposite page). In this case, you may connect the ground wire from the wiring harness directly to the soldered wire, and it would provide the best ground connection you could have.  The sealing of the cork gasket and the small rubber sealing rings would insure a gas tight connection as well.

Now that we’ve considered the connections at the rear of the car, we should move forward, along the wiring harness path, to the connections at the instrument panel and gauge housing.  Within the loom are several soldered ground connections. These are shown on the wiring diagram.  In all my years working on automobiles, I have never found an occasion where one of these factory-assembled harnesses have separated, except in the case of a mechanical impact, or an electrical fire. This doesn’t mean it couldn’t happen, but I wouldn’t look there first.

The mechanical connections between the fuel gauge housing and the instrument cluster itself, and between the ground wire and the cluster housing, are just as important as any other we have considered. This ground wire is difficult to see, and often ignored. It must have a very good, clean, tight connection to the assembly in order for the instruments and lights to all work properly; I always use star washers on this connection.

There is another ground wire attached to the back of the heater/clock console plate. It has nothing to do with the gasoline gauge, but it is necessary for the proper operation of the heater blower motor, which is grounded through the Bowden cables to this plate.  The clock and clock lamp are also grounded by means of this wire.  The radio has its own separate ground wire. It is connected to the radio mounting bracket bolt and extends through the firewall where it connects to the righthand engine valve cover rear inboard screw.

The entire wire harness ground circuit terminates at one point. Perhaps this is part of the problem. It is all tied together and makes one major connection at the left-hand valve cover rear inboard screw.  This screw is often found to be loose. I would use the toothed washers on each side of the terminal of this wire to insure good electrical contact. I check this connection often because it’s so important.

We still have to consider one more area of great importance. That area would be the main engine ground.

Keep in mind that every ground wire discussed to this point has been ultimately connected to the engine. Since the engine uses rubber mounts, as is the transmission and exhaust, the entire assembly must be properly grounded if all this is going to work. This is done by the negative battery cable connected directly to the engine at one of the starter motor attachment bolts. Once again, I always use a star washer on each side of the cable end where it connects to the starter. This allows for the cable to make a good electrical connection to the starter and the starter attachment bolt, which is screwed into the threads of the bell housing.

I’ve been able to correct the “Dancing Gasoline Gauge” troubles by checking and correcting the various ground connections discussed.  If you have any other tips, feel free to call me.

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