How Tos

How to Diagnose Automotive Electrical Ground Issues

(Image/Dash Cam Store)

Chasing down electrical gremlins in a motor vehicle can be an exercise in frustration—the kind of frustration that makes young men old and old men talk to themselves.

An electrical problem can often be traced to a single source: a bad ground connection. A bad ground can cause noise in an audio system, make electric fuel pumps run hot or produce low pressure, and make electronic engine controls do weird things.

Make Sure You Have a Quality Ground Point

Many think that as long as the accessory’s ground wire is touching some part of the vehicle, it is grounded. That is not the case. You must make sure the ground wire is attached at a point that is free of paint, rust, or plating. Paint on body panels and the engine acts as an insulator, resulting in a bad ground connection.

Best Practice for Grounding Accessories to an Engine

If you are grounding an accessory to the engine, it’s good practice to run a ground wire directly to the alternator case and make sure there is no paint between the starter and the engine block mounting surface.

Using a Voltmeter/Multimeter to Test the Connection

If your accessory still doesn’t work properly after redoing the grounds, you will need a voltmeter or multimeter to trace the wiring. Set the voltmeter to read ohms (resistance) and probe the battery’s negative stud and ground connection on the accessory (the ground terminal on an amp, for example). If you have a reading less than five ohms, the ground is okay.

If the resistance is okay but the accessory still isn’t working right, set the voltmeter to DC current (voltage). Turn the accessory on and retrace the grounding path as you did before. The voltage should be no greater than .05 volts under load. If you find a point where voltage is present, then you need to add a bonding strap or find a new grounding point so no voltage is present at any of the grounding points.

If the reading is higher, you need to probe the grounding path between the accessory and the battery. Starting at the battery, run the voltmeter probe from the battery to the first grounding point, usually a fender on muscle cars and trucks. Continue to where the fender attaches to the main body, and from there to the accessory. If you find a point of high resistance (over five ohms), you will need to attach a bonding strap or wire between the panels or parts where resistance is highest.

Consider Engine-to-Chassis Ground Strap

One of the best things you can do to help ensure a properly grounded vehicle is to replace or add an engine-to-chassis ground strap; Taylor makes a nice four-gauge, braided stainless steel strap ideal for most vehicles.

Consider Larger Gauge Wire

If you are adding a number of accessories or ones that draw a large amount of current, you should also replace the battery-to-chassis ground with a larger gauge wire. That’s because the factory ground wire is usually a less-than-adequate 10 or 12 gauge. A ground wire must be as large as the positive, or supply, wire to the battery.

Hopefully you will never have to experience the joy of tracing a bad ground. But if you find yourself in such a situation, these tips will help make the job go smoother—and get your ride back on ground level.

For more information on the basics of automotive electrical troubleshooting, check out our friend Eric the Car Guy’s two-part video series covering it:

Electrical Troubleshooting Basics, Part 1

Electrical Troubleshooting Basics, Part 2

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None of your electrical stuff will work properly without being grounded to some point on either the vehicle or the engine. Take your audio system as an example. The best way to ground a system is to connect the ground terminals of all components to a common ground wire. That wire should be routed to a grounding point on the negative side of your vehicle's electrical system—the negative side of the battery is a good choice. Also, make sure the grounding point is free of paint, rust, or plating, which can prevent a good ground connection.

If you have a lot of accessories or ones that draw at lot of current, replace the battery-to-chassis ground with a large gauge wire or strap like this Taylor Diamondback braided ground strap. The strap is also ideal for grounding the engine block to the chassis. Many vehicles had an engine to ground strap from the factory; it's a good idea to check the stock strap and replace it if it is damaged or frayed.

A good ground is especially important with engines that are electronically fuel-injected or have some other type of computer control or digital ignition system. Aftermarket wiring harnesses have ground connections built into them, making the grounding process a no-brainer. Painless Performance has universal and application-specific harnesses for fuel injected engines, plus complete vehicle harnesses for muscle cars, street rods, and race cars. Tip: never use a test light to check computer-controlled components. Not only is a test light inaccurate, it will destroy the components. Use a good voltmeter or multimeter instead.

If you work on electrical systems often, a multimeter like this Sunpro Auto TroubleShooter is practically indispensible. You can use it to locate faulty wiring, test electrical components, engine sensors, ignition and fuel systems and starting/charging system voltage. Here is a sample of what the multimeter can check: *Engine RPM and dwell *AC/DC voltage, DC current and resistance *Diodes and continuity *Starting/charging, ignition and fuel delivery systems *Locate faulty wiring and components The Sunpro Auto TroubleShooter runs on a nine-volt battery, has an easy-to-read digital LCD, a hold button to retain display data, automatic reverse polarity indication, and automatic zero adjustment for volts and amps for accurate measurements.

This Actron AutoAnalyzer multimeter does most of the same testing that the Sunpro Auto Troubleshooter does, but costs a little less. It performs all standard electrical tests for on-car and bench troubleshooting. It has a backlit LCD for easy reading, color-coded detachable test leads, and alligator clips for hands-free test lead connections.

Parts List

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12 Comments

  1. Chuck Grover Jr says:

    A very good read Dave thanks

  2. Hey Dave, Got a question. I’m new to the electrical side of automotive. I just got a multimeter to troubleshoot and hopefully pinpoint my problem. As it’s hard to find a trustworthy mechanic who knows jeeps or a affordable diagnostics scanner (tried cheapys) That works with my 2005/06 Wh/Wk jeep grand Cherokee (I’m in Aus btw). I can’t afford to throw money at it without actually fixing the problem. I have driven 2years over 10000kms with abs,tcs lights on dash. Went in limp mode occasionally and park brake/e-brake light comes on dash. So done new battery, front hubs, all WSS sensors. But now it’s stuck in limp mode with e-brake light on dash (tried new switch). I’m waiting on brake shoes but old’s work fine. Also waiting for pads rear are 50% front 70%. I’m trying to find out if the hydraulic brake pressure switch is +or- I can’t get clear answer or diagram online to clarify circuit. There is no power to e-brake wire is this wrong? Should it have power til grounded? Is circuit broken by brake pressure switch? The fluid level wire has power which I thought was on same circuit. I can’t get brake booster switch off to test. Any info would be appreciated
    Thanks

  3. Ok i ran across this. I had a dead battery rwo days ago and so had a new one put in. Now when i turn my headlights on it dims the panel inside the car but when i turn the headlights on the panel goes bsck bright. Ive had the new battery checked and the slternstir and they both read good. Im a senior citizen livibg off social security. Can you make recommendations? The shop said my two connectors looked goid and were tight. I have a 2013 mazda 3.

    • Im not really a mechanic, but i am an electrical that has been working on cars for the past few years. Short Answer. Who knows. If you don’t want to do it yourself there are specialists (auto electrical tech). You want to do it? Go back to the battery, is it to strong or to weak. check specs to what you have, connections, battery wires. From there it’s all money spending time. I would replace the alternator then take it to the shop. then another shop for a second opinion

  4. Carolyne O'Callaghan says:

    Hi there

    I have a 2018 Mercedes C Class and last weekend all of a sudden it just died whilst I was driving it. All the lights on the dash came up and all these warning signals. It would start up again but the techni guy that came to it said it was too dangerous to drive. It’s still at the garage now and they said their words to me were that it had had a catastrophic failure and it would take them some time to work out what had caused it to just stop running. Next day they call me back and said that that think it wasn’t earthed properly at manufacture. He also said that he is assuming it is that. They reckon it’s fixed up but they can’t guarantee it won’t happen again – so how does that leave me driving 110 down the highway and it happens again. Does this sound like a car that hasn’t been earthed properly – if it hadn’t been since manufacture why hasn’t it happened before now. Hope you have some idea

  5. I am trying to troubleshoot a 2005 e320 that throws obd fault codes which can’t possibly be valid. I have replaced a few of the sensors but the same faults reappear shortly. The only thing in common with all the sensors is battery voltage and ground. I found a corroded ground strap from transmission to the body. I suspect that this is part of (if not all of) the problem. I have purchased a new ground strap from the dealer but before installing it, I need to know if the new strap and lug bolt should have any anti-seize or grease to retard future corrosion. Will this degrade the quality of the ground connection?

    • vincent colangione says:

      Use a dielectric grease to prevent corrosion. Remember, a electrical connection can be physically tight but may not be electrically tight!

  6. Jon VanDeWiele says:

    I have a 97 ford f150 with a 4.6 in it. I have a grounding issue I think. When I open the door of it the dome light flashes on and off until I close the door. This happens with the truck on or off. Any ideas?

    Jon vdw

    • I certainly would start with checking the body grounds. There should be a wire that comes off the negative cable that bolts to the fender. Remove the bolt from the fender and sand the area back to bare metal, then replace the wire with a dab of dielectric grease on the contact surface. Myself, i would get some 10awg wire, a couple ring terminals, and add it to that body ground. The truck is 23 yrs old, have the battery cables ever been replaced? They do go bad after a while. The wire and ring terminals will be less than 20usd, both cables for the battery will probably be around 70usd(im just guessing there). This has a good chance of clearing up alot of electrical issues you may have

  7. You made a good point that something as simple as paint getting in the way can cause some electrical interruption in a car. I’ve only started driving my new car six months ago and it’s my first time driving an automatic transmission car so it’s kind of difficult for me to troubleshoot electrical problems. I hope I can find an automotive repair service near me this weekend so that I can figure out what’s the deal with my my car shifting gears a bit late.

  8. Craig Evans says:

    I have a 2002 Saturn sl1 my transmission is shifting really hard I ran code test at auto zone only one code U1300 class 2 short to ground. How do I fix this? What do I do next?

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