Learning how to fix a bad ground connection is easy and, in most cases, doesn’t take a lot of time.
As mentioned in one of our previous articles, the more complicated part is finding and recognizing the problem. If you want to learn how to that, click here to view the article.
As you’ll see, fixing a bad ground connection isn’t needy in terms of tools and doesn’t demand a high level of car knowledge. This makes it, in most cases a DIY job.
So, hopefully, this article will give you some guidance on how to solve this problem.
Besides this article, you can watch a YouTube video tutorial at the end of this article or on our YouTube channel.
LOCATION OF GROUND CONNECTIONS
You can’t fix what you can’t find.
Having some prior knowledge of the locations will be a huge help in learning how to fix a bad ground connection. Besides that, it will also spare a lot of time.
The best places to look for these locations are the car manual, Google, YouTube or else.
We’ll go one connection at a time:
The connection from the battery terminal to the car body
You’ll easily recognize it as a thick cable going from the minus battery clamp on one side and to the car body on the other.
The cable is held to the car body with a screw or nut and has black insulation on it.
This is standard for almost all cars so it’s easy to find.
The connection from the car body to the engine or transmission
This connection is recognized as a thick cable (like for the battery connection) or a copper braid (better known as a ground strap) that is connected from the car body to the engine or transmission.
It’s usually in the lower part of the engine bay, somewhere around the gearbox. It will be held in place with nuts or screws (13 and 17 mm is common).
Unlike the previous connection, finding this one can sometimes be tricky. In some cases, you’ll have to go under the car to access it.
Older cars might even have an additional ground cable or strap. This may have been done in the past to improve or completely replace the old connection.
Other ground connections on the car
These are mostly located on various parts of the car body (passenger cabin, trunk, and else) and follow the electrical wiring installation.
They usually look like clusters of multiple wires tightened to the car body with nuts or screws.
Unlike the previous two, the locations of these connections are harder to find and drastically vary from one car model to the other.
Most of them are buried under plastic trimming, carpets, plastic panels in the passenger cabin or the trunk. Finding and reaching them can be a very painstaking and time-consuming job.
This is why previously knowing the exact locations will make the problem, much, much easier to solve.
Wire connectors, among others, contain ground connections. They are best recognized by the color of the wire (most common is black or brown).
To determine the exact wire, best use a multimeter, tester, or wiring diagram.
Another way is to check the connector closest to the problem. For instance, if the rear lamp is causing problems, look at the lamp connector first.
Have in mind that there are also other connectors lower in the wiring installation that can also cause bad ground connection problems.
HOW DO YOU TEST FOR A BAD GROUND CONNECTION?
Before you start thinking about how to fix a bad ground connection, you must determine that this is the actual problem.
Here are a few common ways to do this:
Use a multimeter
This is perhaps the best and most accurate method. You can do this both when the engine is off and on. When the engine is on, you can get more accurate results.
1. Set the multimeter for 12 volts direct current (if the installation is 24 volts, set to 24 volts).
2. First measure the voltage between two battery terminals (they should read about 12.5 volts when the engine is off or 14.5 volts when the engine is running). Red is plus, black is minus.
3. Take off the minus tester and connect it to the car body while leaving the red tester on the battery terminal. Find a clean metal surface or, like in the picture, use the body ground connection.
4. To check the engine ground connection, connect the minus tester to a clean surface on the engine.
4. Where the voltage is lower, that’s where the problem is. For example: if the voltage on the battery is 12.5 volts and the voltage between the battery and the car body is 10 or 11 volts, the body connection is the problem. The same goes for the engine.
To simplify, the voltage difference helps pinpoint the problem and opens a path to a possible solution.
You can do the same check on the wiring installation provided that you can find a positive (+) power source on the car near the problematic connection. Best us a multimeter or tester.
Visual and manual inspection
In some cases, if your lucky enough or if you don’t have a multimeter you may solve the problem with some old-fashioned visual and manual inspection.
Take a look at all the mentioned connections. Look for rust or any kind of damage. Wiggle all the cables and connections and see if they’re tight enough.
In case of heavy cranking or low alternator voltage output, go for the main ground connections first (to the car body and engine).
With electronic glitches, you can try the main connections first but the solution will probably among the body connections or connectors in the passenger cabin, trunk, or else.
In this case, again, it’s very useful to know all the ground connection locations as well as have some basic knowledge of what is connected to what.
Use a jumper cable
This is a simple yet very effective method. All you’ll need is one jumper cable.
You need the cable to directly connect the minus terminal of the battery to either the car body or engine.
The point is to make a direct connection and circumvent the ones on the car.
By doing this you can instantly see what and to some extent where the problem is.
For instance: if you connect the cable to the car body and the problem vanishes, check the connection from the battery terminal to the car body.
If you connect it to the engine and a bad ground connection disappears, you should check the strap or cable between the car body and engine.
It’s sort of a crude elimination process.
It will also give immediate results like with the problem of heavy cranking. By connecting the jumper cable, the engine will be instantly grounded and start to crank without any problems.
By learning how to fix a ground connection this way, you can even help yourself if this happens on the road.
The downside is that it can’t help with more complicated problems like electronic glitches where other peripheral ground connections cause problems.
When doing this, be sure to connect the jumper cable to a clean mechanical metal surface on the car body or engine (various screws, brackets, holders, etc). Don’t connect to any electronic parts even if they have a metal housing.
HOW TO FIX A BAD GROUND CONNECTION?
Solving a bad ground connection is, in most cases, simple.
Regarding tools you’ll need a wrench, ratchet with the proper socket, or screwdriver to tighten or loosen the nuts or screws. For cleaning, you’ll need some contact spray (or WD-40), sandpaper, or a file.
This fix is harder if the ground connection is less accessible (like with the engine connection). Sometimes, in order to reach it, you’ll have to go under the car or take off plastic protective coverings.
Now for the solutions:
Tighten loose contacts
Use the wrench, ratchet, or screwdriver for this task. Make sure that every connection is nice and tight.
If you see any damaged screws, nuts, or threads replace them because they may cause loose connections in the near future.
Also, use spring washers if possible. They will prevent loosening as well as provide better contact.
Clean rusty contacts and connections
If you see any sign of rust on the connections, loosen the screws or nuts holding them and thoroughly clean everything. Use contact spray, WD-40, sandpaper, or a file.
When cleaning the ground connection from the battery to the car body, clean both the battery terminal clamp and wire lug on the other side. Also, make sure the connection on the car body is also shiny and clean.
With the ground strap, best to take it off completely. Clean both ends of the strap or cable as well as the metal surfaces.
The other, peripheral ground connections are solved basically the same way. Take off the screws or nuts, clean the wire lugs, and especially the connection to the car body. For this task best use some sandpaper or even a file if the rust is more severe. After that use some contact spray to remove any leftover rust residue.
Also, if the screws, nuts, or washers are very rusty, corroded, or damaged in other ways, best replace them with new ones.
If the wire connectors are causing problems, take them off and use contact spray to clean them. A small screwdriver, scalpel, or sandpaper may come in handy to scrape the contacts. When the connectors are badly damaged, best replace them with new ones, if possible.
The end result must be a tight, spick and span connection where ever it’s located.
Replace damaged cables, straps, or wiring
Any kind of damage on the wire installation should be replaced to avoid immediate or future problems.
Look for tears in the cable or strap, weak or broken connections between the cable and wire lugs, weak contact on the wire connectors, etc.
The best remedy for this problem is a complete replacement, especially with ground cables and straps.
To be honest, there are mending techniques (replacing the wire lugs, soldering, welding, and else) that are also quite effective providing you have the right tools and knowledge to do it. Otherwise, the repair is short-lived.
With ground connections on the wiring installation, a simple replacement of a wire, wire lug, or connector usually solves the problem.
Adding additional ground connections
If cleaning and tightening didn’t help or when a bad ground connection is hard to access this a good solution.
The connection that’s usually added is between the car body and engine. This is a common sight for cars that don’t have ground straps or cables installed at all. The various screws, nuts, and parts of the undercarriage that provide a connection from the car body to the engine may loosen or get rusty over time and lose contact.
So, instead of searching for the fault, a quicker and better solution is adding a new ground connection.
The procedure is to use a cable or strap (best a new one), find a convenient place between the engine or transmission and the car body, and fasten it.
Another common place for adding ground connections is the wiring installation. As mentioned, finding a bad connection, in this case, can be a painstaking job.
If the circumstances allow, you can add a new connection (drill a hole in the car body, use a convenient spare thread or else) and get the same or even better results.
Although it may seem like an improvisation, it’s common practice when solving these kinds of problems.
Knowing how to fix a bad ground connection will come in handy sooner or later. It can save you from unneeded and often expensive repairs caused by this problem.
It’s a simple fix and one that you can do on your own and in a matter of minutes, with only the basic tools.
Problems may be caused by crammed engine bays and ground connections inside the passenger cabin and trunk. Here you have to do some additional dismantling to reach the connections.
But even this isn’t a big problem if you know where the connection is located precisely.
Again and I can’t emphasize this enough, recognizing the problem is the main task. Once you’ve done that, it would be a shame to lose money and time on some cleaning, tightening, or replacing a few parts.
Written by: Sibin Spasojevic
Former car technician, life-long car and DIY enthusiast, author for Despairrepair.com
BAD GROUND CONNECTION YOUTUBE VIDEO