How Tos

How to Diagnose Electrical Ground Issues


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.

But many times, an electrical problem can 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.

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.

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.

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 OK.

If the resistance is OK 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.

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.

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.

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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
Sunpro AutoTroubleShooter Digital Multimeter (SUN-CP7677)
Actron AutoAnalyzer Multimeter (SUN-CP7665)
Taylor Braided Engine Ground Strap, Four-Gauge, 14-inch (TAY-148014)

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  1. My opel, gauges fall while riding then afterword the car doesn’t want to start! Most of the time, after we press buttons on key and unlock and lock a few times it comes right! But happens alot!

  2. I’ve got to say you have a good thought process but you’ve missed the boat and I think you’re misleading people. 5 ohms is way too high, while 50mV is way too low, and DC current is NOT the same as DC Volts.

    • David Rushka says:

      Not arguing, but what do mean its different? Are just referring to current actually being “power used” which would be measured in wattage and voltage being strength of available power? If you are making a different point I’m beyond curious to learn it.
      Thanks in advance!

      • Sorry for the late reply, apparently the site doesn’t send notice of new comments and I didn’t see your question until I happened across the article again. Voltage and Current are different in a couple of ways. It’s a different setting on the multimeter, and it’s a different unit of measurement. Wattage isn’t directly related and is another unit of measure. I say it isn’t “directly” related, because they are all connected, a change in one will change the others. The best way to understand this is to understand Ohm’s Law. Take a look at this video, it gives a good explanation.

  3. Has my question been answered??? I’m really goin nuts with this car! Pls help! My gauges keep falling while riding, and when I stop the car doesn’t want to start until I do the following….lock and unlock the car using the buttons on the key, which works most of the time…or disconnect the battery which sometimes works!

    • Jordan Bruyere says:

      Yes. Has someone recently done any electrical work on your car? In the dash or door panel maybe? Because if they changed like a window regulator or something and it has a bad ground in your door I’m sure unlocking it and locking it can recreate the conditions that makes the ground connect or disconnect. Ground wires can make your car act possesed! I am kind of experiencing similar problems but they are of my own doing. I recently did a head gasket job on my 02 Impala 3.4l v6. Now all my electrical is all out of whack, I turn the key and it just clicks and goes crazy (starter won’t click, just the relays). It started once since. But after doing a few tests I have concluded its a bad ground wire somewhere. (The whole wiring harness had to come off so there’s a list of wires it may be) when reconnecting everything I assume insulation cracked on a wire or one of my connections has gone bad over time and it’s a coincidence that it’s acting up directly after the job.

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