Mailbag: Quick Guide to Electrical System Grounding

Q: Electrical is not my strong suit, but the time has come for me to complete the wiring on my latest project. Electrical systems can be extremely complex, but are there any basic tips you can share to get me going in the right direction? I am particularly concerned about establishing a good, solid ground to avoid any persistent electrical gremlins down the road. Thanks for any help!

A: Without question, modern automotive electrical systems have become extremely complex, and now more than ever, the health of your vehicle’s direct-current (DC) electrical system is dependent on solid electrical grounding.

In its simplest form, the flow of DC current starts at the positive terminal of your battery, moving in one direction through a wire to a device, returning to the battery’s negative terminal via a system of chassis, body, and engine grounds. If the grounds are faulty or non-existent, the circuit is incomplete and current cannot easily (if at all) return to the battery. The current will look for a new path to ground, and this can lead to a host of electrical performance issues.

When you wire up your project vehicle, it’s best to run a cable from the battery’s negative terminal and attach it directly to the engine block. Next ground the frame to the engine, the body to the frame, and the body back to the engine.

Whenever possible, grounding connections should be made to metal surfaces that are free from rust, dirt, chrome plating, powdercoat, and paint. Adding dielectric grease to your connections can stave off corrosion.

You should also know, painted, powdercoated, or chrome brackets can interrupt the ground connection between the alternator and the engine. It’s a good idea to run a supplemental wire from your alternator case to a central grounding location. Some alternators even come with dedicated grounding points.

Additionally, accessories that draw a large amount of current, like electric fans and auxiliary lights, should be individually grounded with a wire matching the size of the electrical supply wire. A Ron Francis Wiring grounding terminal strip is a great choice for organizing supplemental wiring.

Whether you’re planning the electrical system for your project or troubleshooting your existing wiring, it’s important to identify the source of the electricity and ensure there is an unimpeded path to ground. A multimeter that reads DC voltage and resistance and can identify low amp draw is an essential tool for diagnosing just about any electrical gremlin lurking in your vehicle’s wiring system.

For more tips, see our original post on automotive wiring basics.

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This is another in a series of weekly Q&A Mailbag sessions with Summit Racing‘s tech department, in which there are hundreds more. Click here to see them all.