Before You Run That New Ground Wire

automotive wiring
Wiring is a snap once you understand the concepts. Getty

Outside of checking for a bad fuse, electrical troubleshooting can be a bear, but it’s the only way you’ll figure out what’s wrong with a piece of electronics or a power window in your car or truck. Testing your electrical circuits is crucial to figuring out why something has stopped working. Often, you’ll discover that the source of your ill-behaving electrical component was something as simple as a loose wiring harness or a bad ground connection.

The loose wiring harness fix is pretty easy, but what do you do if you test your ground wire and discover that you aren’t grounded? An electrical component that isn’t working at all could have a bad ground, and if you’ve already tested the power supply and discovered it to be hot, you’ll move to testing the ground. No ground means no nothing in an electrical part. 

Before I tell you how to fix or replace the ground wire on most electrical wiring harnesses, you should understand what a ground does and why it’s so easy to replace it, much easier than replacing a power wire or pretty much any other wire in your car. You can also skip to the bottom and just learn how to fix the bad ground wire. Understanding an electrical circuit can be complicated, but for the purposes of doing simple repairs on automotive wiring, there are only a few things you need to know. The positive side of the wiring is super complex, the ground side usually super simple.

While the positive side of the wiring has a series of switches, relays, fuses and plugs that carry the electricity from the battery or alternator to the various electrical components, the negative side of the wiring goes from the component to pretty much any piece of metal that’s permanently attached to the car.

It’s not that simple 100% of the time, but almost always. If you have a car or truck that allows you to see the battery, take a look. you’ll the the positive side of the battery with a number of wires attached to it, leading to different things. The thick one goes to your starter, others go to different fuse boxes, and so on. But if you look at the negative (or ground) side of the battery, you’ll often see only a single wire which, if followed, leads to a giant bolt that attaches it to the heavy metal chassis of your car or truck. Attaching the battery’s negative side to the chassis of the vehicle means that the entire chassis, and anything metal that’s attached to it, becomes an extension of the battery’s negative side. So anything that needs to be attached to the negative side of the battery can now be screwed or bolted onto any grounded metal. It’s an ingenious system that works very well in a car or airplane where weight is a factor. Imagine how much your car would weigh if it had as much grounding wire as it has power wire. 

That’s why it can be so easy to repair a faulty ground wire! If you’ve tested the wiring on a malfunctioning electrical component and found that it does not have a good ground, you can run a new ground wire without tracing wiring all over the place.

Before you start snipping wires, be sure that you know what’s what by consulting the wiring diagrams (also known as hieroglyphics) that are contained in your car’s repair manual. You won’t find them in your glove box owner’s manual, you’ll need the real deal repair book. Once you are one hundred percent sure you are looking at the ground wire, you can snip it and strip it.  You’ll be taking this wire on a different journey to ground.