Rick's Free Auto Repair Advice

erratic gauges

How to fix erratic gauges

I see lots of posts on car forums where the poster has really strange electrical problems like erratic gauges or the the blower will only work when the brakes are applied, or lights work only when certain other electrical accessories are either on or off. Most DIYers automatically assume these electrical problems are caused on the power side of the electrical device. In almost all cases, it turns out to be on the ground side.

Car makers install multiple grounding points in every vehicle. They use the metal body as the return path back to the battery. That’s a bad idea—always has been, always will be. Because any time you try to run electrical energy through multiple steel panels that are exposed to humidity, you’re going to get corrosion. And, if the electrical energy can’t return through one ground path, it’ll find another.

So if you have erratic gauges, ALWAYS suspect a bad ground if you’re getting strange electrical operation. Here’s the best way to test. Get a jump wire with alligator clamps on each end and supply a new ground from the electrical device to the nearest clean metal ground. If the device works, you’ve diagnosed the problem. Next, get a good shop manual and download the wiring diagram for that electrical device. The diagram will show you where the ground point is. Then disassemble the ground connection, clean it with sandpaper or wire brush, and then reassemble it. Coat the entire connection with dielectric grease to prevent further corrosion.

If the ground connection runs through an electrical connector and the connector is corroded, read this post on how to clean it.

© 2012 Rick Muscoplat

Posted on by Rick Muscoplat


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