There is every reason to make sure that the car battery wire connections remain cool as high temperatures can lead to a fire.
Unfortunately, it is not always possible and you may have a situation where for instance, the negative battery ground wire gets extremely hot to the touch while attempting to start the car.
What causes this and how do you go about fixing it? Is it even an issue that you can fix yourself?
The aim of this post is to answer these questions and more and equip you with the information that you can use to quickly identify and fix the underlying issue and avert a possible fire.
Reasons Why the Car Battery Ground Wire often Heats up (+Solutions)
If the car battery ground wire temperature is extremely high while starting the car or the engine is running, check the following:
#1. The ground wire connections from the battery negative to the fender or engine block may be loose. Loosely connected ground cables have a smaller contact area which coupled with the high current flow as the car starts up causes the wires to get extremely hot.
Inspect each of the ground wire connections from the battery to the fender and from the fender to the engine block.
Make sure they make clean and firm contact. Connections to the fender should be made to the unpainted part of the fender for good electrical connectivity.
#2. Ground wires may be corroded or broken inside. Wire connections can appear intact on the outside but damaged on the inside. To test whether the ground wires are intact you can conduct a voltage drop test on the negative battery terminal.
Using Voltage Drop Measurements to Confirm Alternator Ground Connections
What you need: A good quality multimeter set to read DC voltage
- With the multimeter set to read DC voltage, connect the positive lead of the multimeter to the negative battery terminal and the negative lead to first, the exposed part of the car fender and next to the engine block.
- Next, start the car engine while taking a DC voltage reading first with the connection to the car fender and then the engine block as laid out above. The voltage drop in each case should be 0.2 V or less for a good battery ground.
A higher voltage drop indicates a high resistance connection in the grounding path.
Make sure that the ground wire connections are clean and firm. You may need to replace the ground wires if the high voltage readings persist even after confirming that the wire connections are clean and firm.
#3. The battery ground wire may be undersized. Have you replaced the factory battery cables including the ground wires recently?
Undersized ground wires overheat when the current flow is high.
Is this Normal?
No, it is not normal that the ground wire connections are hot. This is indicative of a grounding fault and a high current flow over the limits of what the ground wire can handle. In extreme cases, this may lead to the wires melting.
Check the possible reasons and fixes why the ground wire connection may be getting extremely hot.
Symptoms of a Bad Car Battery Ground Wire
Note: These signs are not confirmation that indeed it is a grounding problem as they can be attributed to other causes too.
If there’s an issue with the car battery’s grounding, the car may show the following signs:
- car may struggle to turn over. You may have to make several attempts before it turns over
- the battery ground wires will get extremely hot
- If the car’s electrical accessories operate in an erratic, unexplained way such as lights randomly or intermittently dimming or activating one set of accessories such as a window can instead affect the operation of another accessory.
If your car’s ground wire gets extremely hot or even melts, you should as a start confirm that the wire connections are firm, make solid clean contact, and are intact and that they are appropriately sized.