* Faulty wiper switch: The most common cause. A malfunctioning wiper switch can send power to the wiper motor even when it shouldn't. Internal shorts or wear and tear are the usual culprits.
* Short in the wiper switch wiring: A short circuit in the wiring harness leading to or from the wiper switch can also supply power to the motor unintentionally. This could be caused by damage to the wiring (chafing, rodent damage), a corroded connector, or a poorly repaired previous issue.
* Problem with the wiper motor itself: While less likely, a faulty wiper motor can sometimes draw power even when it's not supposed to. This is usually manifested by the motor running erratically or constantly, not just when the ignition is off.
* Body control module (BCM) issue: The BCM controls many functions in the vehicle. A malfunctioning BCM could be sending incorrect signals to the wiper motor. This is less common but possible. (Your van likely has a BCM, though it might not be called that explicitly in the documentation.)
* Aftermarket alarm or accessory issues: If you've added any aftermarket security systems, remote starters, or other accessories, their wiring might be interfering with the wiper system.
Troubleshooting Steps:
1. Check the wiper switch itself: Carefully inspect the switch for any obvious damage or signs of burning. Try wiggling it gently to see if the wipers react. If possible, try swapping the switch with one known to be good from a similar vehicle.
2. Inspect the wiring: Trace the wiring harness from the wiper switch to the wiper motor. Look for any signs of damage, corrosion, or bare wires. Pay close attention to areas where the wiring might be rubbing against metal parts.
3. Test the wiper motor: Disconnect the wiper motor connector. If the wipers still operate, the problem lies elsewhere in the wiring or control system. If the wipers stop, the motor is likely faulty.
4. Check fuses and relays: Inspect the fuses and relays related to the wipers in the fuse box. A faulty relay could be stuck closed, constantly supplying power to the motor.
If you're not comfortable working with car electrical systems, it's best to take your van to a qualified mechanic for diagnosis and repair. Incorrectly diagnosing and repairing electrical issues can lead to further damage and potential safety hazards.
