1. Check the Fuses and Relays:
* Locate the fuse(s) and relay(s) for the radiator fan. Your owner's manual will show you the location and amperage rating of the fuses and the relay location. Many Mustangs use a relay, sometimes even two (one for high speed, one for low).
* Visually inspect the fuses. Look for blown fuses (a broken filament inside). Replace any blown fuses with the correct amperage rating. Important: Don't simply replace a blown fuse without finding out *why* it blew. Replacing it with another fuse of the same rating might just blow again immediately.
* Test the relays. You can do this a few ways:
* Visual inspection: Check the relay for any obvious damage.
* Using a multimeter (best method): With the ignition ON, check for power at the relay's power input and ground. Then, check for continuity between the relay's coil terminals (when the relay is unpowered). If you don't have a multimeter, move to the next step.
* Swap the relay: If you have a spare relay of the same type, swap it with the fan relay. If the fan starts working, the original relay was faulty.
2. Check the Fan Motor Directly:
* Disconnect the fan's electrical connector.
* Use a multimeter to test the fan motor directly. Set your multimeter to measure resistance (ohms). Connect the multimeter leads to the fan motor's terminals. You should get a reading in the range of a few ohms. A high resistance or open circuit reading indicates a faulty fan motor. A reading of zero (or very low resistance) could suggest a short circuit.
* Apply 12V directly to the fan motor (with caution). Only do this if you're comfortable with working with electricity and the fan motor is disconnected from the vehicle's electrical system. If the fan works, the problem is likely in the wiring or control circuitry. Use caution, because the fan will immediately start spinning at full speed. Wear safety glasses. This method should only be used as a last resort before replacing the motor.
3. Check the Wiring:
* Inspect all wiring related to the radiator fan. Look for any broken, frayed, or corroded wires. Pay close attention to the connections at the fan motor, relay, and fuse box.
* Use a multimeter to test for continuity in the wiring. You should have continuity between the battery positive, the fuse, the relay, and the fan motor.
* Check the ground connection. A poor ground connection can prevent the fan from working. Make sure the ground wire is clean and securely attached.
4. Check the Cooling Fan Control Circuit:
This is more involved and may require a wiring diagram for your specific year and model Mustang. The fan's operation might be controlled by:
* The PCM (Powertrain Control Module): This is the computer that controls many aspects of the engine. A faulty PCM or a problem with the PCM's programming can prevent the fan from turning on.
* A temperature sensor: The fan is usually controlled by a coolant temperature sensor. A faulty sensor might not be sending the correct signal to the PCM to turn on the fan.
* Other sensors (some models): The A/C system might also control the fan, so a problem in that system could affect fan operation.
5. If all else fails:
Take your Mustang to a qualified mechanic. Diagnosing electrical issues can be complex, and a professional will have the tools and expertise to pinpoint the problem.
Remember to disconnect the negative battery terminal before starting any electrical work to prevent accidental short circuits. Always consult your owner's manual for specific information about your vehicle's electrical system.
