The alternator output wire keeps the battery charged and supplies the electricity to keep the car’s electrical system working as the car engine runs.
Therefore it is important that the output wire from the alternator to the battery remains in good working condition for the safety and continued performance of the car’s electrical system.
Should it become extremely hot or even melt, get to the underlying reasons and fix them right away. This post explains why it happens and what you can do to fix it.
Reasons why an Alternator wire Becomes Hot
First, check if the entire length of wire from the alternator to the battery is hot or if it is hot at the connection point either at the alternator or battery.
Case 1: If it is the length of the alternator wire to the battery terminal
It’s probably because there is a loose wire connection at the alternator or battery that is sparking and leading to heat buildup at either the alternator or the battery.
Inspect the wire connections at either the alternator or battery wire checking for loose or frayed wire connections.
At the alternator end, make sure there’s no short between the alternator terminal and the casing. Replace any burnt terminals and make sure the output wire makes firm, solid connections on either side.
You may have to cut back any damaged wire sections to use the same wire or replace the entire length of wire with another of the same gauge.
Case 2: When the entire alternator wire is hot
If it is the entire length of wire that is hot, it might be because:
#1. Faulty battery. A battery with a shorting cell can draw an unusually high current from the alternator that what the available alternator to battery cable can safely handle easily hence the heat buildup.
Is the resting voltage of the battery about 12.6 VDC or does it drop considerably even after being fully charged?
If it does, the car battery may have a shorting cell. You can use a portable battery tester or have the battery tested at a car auto parts repair clinic.
#2. Check that the battery connections are not interchanged (reversed) as this too can cause the alternator wire to become extremely hot.
#3. There’s a short-circuit in the car’s electrical system
A short in the wiring of the electrical system can also lead to a high current draw and overheating in the alternator.
This short might be along the cable length, in the wire harness, or it could even be a case of wires exposed following the melting of the insulation touching each other.
To check if there is a short circuit, disconnect the battery cables from the battery and measure the resistance across both cables. A zero resistance points to a short-circuit in the wiring that needs to be investigated.
You can work backward from the battery cables toward the alternator to locate the short circuit. Do not hesitate to consult a qualified auto mechanic for assistance.
#4. The alternator to the battery wire is undersized. if there’s an undersized alternator cable then it will become hot as the current flowing from the alternator increases.
Might you have recently changed the alternator wire? Or perhaps upgraded the alternator to a higher amperage alternator?
If you upgraded the alternator, you may need to use a thicker wire. It should be able to handle the full amperage of the alternator usually AWG 4 or larger.
What Cause the Alternator Wire to become Hot, Burn and Melt?
If the alternator wire melts and burns it is usually a case of an undersized wire or a short in the alternator output.
A short in the electrical system can also result in a high current draw and overheating in the alternator. This short be along the cable length, in the wire harness, or it could even be wired with melted insulation touching each other.
How Hot Should an Alternator wire get?
The alternator wire should be slightly warm to the touch when charging the battery. It should not too hot to cause burns.
Should it be Hot? Is it normal?
No, the alternator to battery wire is suitably sized to handle the alternator amperage and should not be hot.
What it Means when the Alternator Wire is Hot
A hot wire points to an excessive current draw over and above what the alternator can handle.
This may be caused by a fault in the alternator, the wire connections, or at the battery. It needs to be addressed immediately otherwise it may lead to a damaged alternator or even a fire.
What Cause an Alternator to Overheat?
There are several possible reasons that can lead to overheating of the alternator. The alternator may be grounded via the alternator case or via the grounding strap. for example.
You can check the quality of the connection by conducting a voltage drop test on the ground circuit.
Voltage Drop Measurements with the Alternator
Connect one end of the voltmeter on the alternator case and the other on the battery negative terminal.
Run the engine at about 2,000 rpm while switching on the lights, radio, and blower. Take the voltage reading. If the ground connection is good, the voltage drop should be less than 0.2V.
This may be because the alternator ground wire is undersized and loosely connected. You may have to run an extra zero gauge wire from the alternator ground to the battery negative to improve the connection.
You may also be interested in this post: 7 Common causes of overheating in alternators
An alternator wire should be warm when you touch it and not hot. If it is hot, then there might be several possible causes that you need to work through – a loose, corroded connection, an undersized cable, or a failing alternator with a high voltage output.
Additionally, if the grounding is bad, you can have an alternator grounding wire overheating and melting.