* Faulty Fan Motor: The most probable cause is the fan motor itself. Internal windings may be shorted or worn, causing a much higher than normal current flow. This is the most common reason for a motor to draw excessive current and overheat its wiring.
* Worn Brushes (if it's a brushed motor): Older fan motors use brushes to transfer electricity to the rotor. If these brushes are worn down, they can create increased resistance and sparking, leading to heat.
* Bad Wiring/Connections: While you're bypassing the car's wiring harness for the direct 12V test, check the wires connected to the motor itself. A loose connection, corrosion, or a damaged wire within the motor's wiring can create a high resistance point.
* High-Resistance Ground: Ensure the motor has a good ground connection. A poor ground can force the current to flow through other paths, generating heat in the wires.
Troubleshooting Steps:
1. Inspect the Fan Motor: Carefully examine the motor for any signs of damage, burn marks, or loose connections. If possible, try measuring the resistance of the motor windings (using a multimeter set to ohms) to see if it's within the manufacturer's specifications (this may require a wiring diagram). A significantly lower resistance than expected could suggest a short.
2. Check Wiring: Examine the wiring between the motor and the point where you're connecting the 12V. Look for any kinks, breaks, or signs of melting. Check the connections for corrosion or looseness.
3. Test with an Ammeter (optional, but best practice): Connect an ammeter in series with the fan motor and the 12V supply. This will measure the current draw. If the current is significantly higher than the motor's rated current (found in the motor's specifications or a wiring diagram), it confirms a problem with the motor or its wiring.
4. Replacement: If you find damage to the motor, wiring, or connections, the most reliable solution is to replace the faulty part. It's usually more cost-effective and safer to replace a faulty fan motor than to try and repair it.
Safety First: Working with electricity can be dangerous. If you're not comfortable performing these checks, take your car to a qualified mechanic. Overheating wires are a fire hazard.
