* Faulty Wiper Switch: The switch itself could be malfunctioning, stuck in the "on" position, or sending a continuous signal to the motor even when you've turned it off. This is a very common cause.
* Wiring Issues: A short circuit in the wiring harness leading to the wiper motor can constantly supply power, causing it to run continuously. This could be caused by damaged insulation, corroded connectors, or a wire rubbing against a metal part.
* Multi-Function Switch (MFS): The MFS is a common failure point in many vehicles. It controls various functions, including wipers, turn signals, and headlights. A problem within the MFS can result in the wipers staying on.
* Wiper Motor Control Module (if equipped): Some vehicles have a dedicated control module for the wiper motor. A fault in this module can prevent the motor from turning off. The 2003 F-150 might or might not have one; this is less likely than the other causes.
* Park Position Issue: The mechanism that allows the wipers to park (return to their resting position) could be jammed or broken. This wouldn't prevent them from running, but if they're not in the park position, the switch might think they're still active.
* Stuck Relay: A relay might be stuck closed, continuously sending power to the motor.
* Faulty Wiper Motor (less likely): While possible, it's less probable than the other issues. A faulty motor is more likely to exhibit intermittent operation or complete failure, rather than continuous running.
Troubleshooting Steps:
1. Check the Fuse: Start by checking the fuse for the wiper motor. A blown fuse could indicate a short circuit elsewhere in the system. If it's blown, replace it, but if it blows again immediately, you have a more serious electrical problem.
2. Inspect the Wiper Switch: Carefully inspect the wiper switch itself. Look for any signs of damage or if it feels loose or sticky.
3. Check the Wiring: This is the most difficult step and often requires removing some interior panels to access the wiring harness. Look for any visual damage, corrosion, or broken wires.
4. Test the Relay (if you can locate it): If you can find the wiper motor relay, try swapping it with a similar relay of the same amperage rating (make sure the amperage rating matches) to see if the problem is resolved.
5. Professional Diagnosis: If you are not comfortable working with automotive electrical systems, it's best to take your truck to a qualified mechanic or auto electrician for diagnosis and repair. They have the tools and experience to safely and efficiently identify and fix the problem.
Remember to disconnect the battery's negative terminal before working on any electrical components in your vehicle to avoid short circuits or injury.
