Nothing is more frustrating, confusing or time consuming than troubleshooting electrical problems. People often think a component is the root of the problem. They replace it, but the electrical issue remains… leading to even more frustration.

Generally, an electrical issue can be traced to a bad ground connection. Poor grounds can cause a multitude of issues, ranging from the very simple to the very complex. A poor ground can overheat electrical components, cause a hum in your audio system, dim your headlights, or even make the left turn signal light up solid when you turn your headlights on! A loose ground can also make it appear that your headlights are bad. When these problems occur, it seems like your whole car is wired wrong… when, in fact, the culprit is just a bad ground.

The number one issue with grounds is a common misconception about how they work: many people think that as long as the ground wire is touching some part of the vehicle, it’s grounded. This is simply not true. When making ground connections, you must make certain that the point of the ground connection is free of paint, primer, rust or other contaminants. These contaminants act as an insulator, resulting is a poor ground connection.

Another potential issue is the length of the ground. Many people tend to run the ground wire too long. Grounding should be performed as close to the accessory as possible. Running longer grounds builds resistance, which builds up heat. This can stress switches and other connections, leading to additional issues.

When grounding under the hood, find a place on the engine block and sand off the paint and any corrosion. Use an external locking star washer to make a tight connection. The star washer helps make a good connection, and it makes certain that it won’t come loose.

If you’ve checked all of your connections, and you’re still having issues with an accessory, you will need to trace the wiring. I use a multimeter. Set the meter to read ohms, and then check the reading at the battery’s negative terminal and at the ground terminal on the accessory. A reading of less than 5 ohms tells you the ground is okay. If you get a higher reading, make a better ground connection.

Next, set the voltmeter to DC current (voltage). Turn on the accessory and trace the grounding path just like before. The voltage should be no greater than .05 volts under load. If there are any points where voltage is present, you’ll need to find a better grounding location, or add a ground strap. The goal is to have no voltage at any of the grounding points.

If the voltage reading exceeds .05 volts under load, you’ll need to trace the grounding path between the accessory and the battery.  Start at the battery. Run the voltmeter from the battery to the first grounding point (usually a radiator core support or fender on older vehicles). Next, trace from the ground connection to the fender/core support connection, and then to the fender to body connection. If you find resistance over 5 ohms, a ground or bonding strap should be installed between the body parts.

Finally, you’ll also want to make sure that your battery ground cable is the proper gauge to handle all of your accessories.  Today, we add a lot of accessories to our cars, and the factory ground straps may be too small of a gauge. When in doubt, upgrade your chassis grounds.

At Capp’s Hot Rods, we always recommend changing (or adding) engine to chassis grounds. And we carry assorted grounds to do just that. One in particular is a braided stainless ground that is the proper size for most hot rods, muscle cars and trucks. Remember, you can never have too many grounds on a vehicle. The real problem occurs when they’re not installed properly.

Oh, and fiberglass cars require even more attention when wiring. Again, more properly installed grounds means less chance of any issues.

Good luck with your project!

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With over 40 years of combined restoration experience, Capp’s Hot Rods rebuilds and restores Model As, Deuces, ’33s and up, classic cars of all makes and models, and muscle cars. Located in Woodland Hills, California, they specialize in complete wiring services, from repairs to complete harness installations. Visit their website or call 818-974-7530 for more information, or to schedule an appointment for your classic car.  You can also find the Capp’s team at the Pomona Swap Meet on Road 22, Spaces 22, 24 and 26.