* Fuse: Check the fuses related to both the cruise control and the horn. Your owner's manual will show you the fuse box location and which fuses are responsible for these systems. A blown fuse is the easiest and cheapest fix.
* Horn Relay: The horn relay is an electromagnetic switch that activates the horn. Sometimes, a faulty relay can also affect the cruise control system's operation, as they might share a common power source or circuit. Locate the horn relay (often in the under-hood fuse box) and try swapping it with a known good relay of the same type (always ensure the car is off before doing this).
* Clock Spring (Spiral Cable): This is a critical component located behind the steering wheel. It's a rotating electrical connector that allows the steering wheel to turn while maintaining electrical contact for things like the horn, cruise control, airbag, and other steering wheel controls. A broken or worn clock spring is a common cause of these symptoms. This is a more involved repair, often requiring steering wheel disassembly.
* Multi-Function Switch (Steering Wheel Switch): This switch contains buttons for the horn and cruise control. A faulty switch could interrupt the signal to both systems. This part is relatively easy to replace, but diagnosis requires checking for continuity and proper voltage.
* Wiring Issues: A short circuit, frayed wire, or corroded connection in the wiring harness leading to or from these components could cause intermittent or complete failure of both the cruise control and horn. This requires tracing the wiring and checking connections, which can be a complex process.
* Body Control Module (BCM): This is the computer that manages many of the car's electrical systems. A faulty BCM could cause various electrical problems, including the malfunction of cruise control and horn. This is the least likely cause without other electrical gremlins, but it's possible. Diagnosing BCM issues requires specialized equipment.
Troubleshooting Steps:
1. Start with the fuses: This is the easiest and quickest check.
2. Check the horn relay: It's a simple swap to test.
3. Inspect the wiring harness: Look for any obvious damage or corrosion near the steering wheel and the fuse box.
4. If fuses and relays are good: Consider the clock spring as a likely culprit. This usually requires professional diagnosis and repair.
Important Note: If you are not comfortable working with car electronics or mechanical systems, it is best to take your Mustang to a qualified mechanic for diagnosis and repair. Improperly working on your car's electrical system can lead to further damage or even injury.
