* Bad Wiper Motor: The motor itself might be failing. The brushes inside wear out over time, leading to inconsistent power delivery and intermittent operation. This is a common cause of intermittent problems.
* Worn or Damaged Wiring/Connectors: The wiring harness leading to the wiper motor can be corroded, frayed, or have loose connections, especially in areas exposed to the elements. This can cause poor electrical contact, leading to intermittent operation. Inspect the wiring carefully for breaks, chafing, and corrosion near the motor and the connection points.
* Faulty Wiper Switch: The switch in the driver's compartment that controls the rear wiper might be malfunctioning. It could have internal wear or a loose connection, causing inconsistent signals to reach the motor.
* Park Switch (if applicable): Some rear wiper systems have a park switch that signals the motor's position. A faulty park switch could interfere with the motor's operation.
* Fuse: A blown fuse in the rear wiper circuit will stop the wiper completely, but a partially blown or failing fuse *could* cause intermittent operation. Check the fuse box for a blown fuse associated with the rear wiper.
* Relay: A relay is an electrical switch that controls the higher current flow to the motor. A failing relay can cause intermittent or no operation.
* Ground Fault: A poor ground connection somewhere in the circuit can interrupt power intermittently.
* Multi-Function Switch (common on Ford): The stalk that controls the wipers and turn signals often contains multiple switches. A problem within the multi-function switch could be the source.
Troubleshooting Steps:
1. Check the Fuse: This is the easiest first step.
2. Inspect the Wiring: Look for visible damage to the wiring harness leading to the motor.
3. Test the Wiper Motor (if possible): This might require some electrical know-how and a multimeter to directly test the motor's operation with power applied.
4. Test the Wiper Switch: This is harder to test without a wiring diagram, but a mechanic or advanced DIYer might be able to do this.
5. Check Ground Connections: Locate the ground connection points for the rear wiper circuit and clean them thoroughly.
6. Relay inspection and replacement (if found to be faulty): This is an intermediate repair that requires basic electrical knowledge.
If you are not comfortable working with automotive electrical systems, it's best to take your Mountaineer to a qualified mechanic for diagnosis and repair. The intermittent nature of the problem makes it harder to diagnose without specialized tools and knowledge.
