* Fuse: Check the fuse box (usually under the hood or in the passenger compartment) for a blown fuse related to the rear wiper. The owner's manual will show you the fuse diagram.
* Wiper Motor: The motor itself might be failing. Intermittent operation is a classic symptom of a motor on its way out. Worn brushes or internal electrical issues are common causes.
* Wiring/Connectors: Corrosion, broken wires, or loose connectors in the wiring harness leading to the motor are frequent culprits. Check the connections at the motor and along the harness for any damage or corrosion. Pay close attention to areas prone to moisture.
* Switch: The rear wiper switch itself could be faulty. Sometimes the contacts inside wear down, leading to inconsistent operation.
* Ground Connection: A poor ground connection can interrupt the electrical circuit. Make sure the ground wire to the motor is securely attached and clean.
* Relay: Some vehicles use a relay to control the wiper motor. A faulty relay can cause intermittent operation. This is less common but possible.
* Park Mechanism: The wiper arm may not be properly parking, creating a situation where the motor is struggling, leading to intermittent function.
* Washer Fluid Reservoir/Pump: Though not directly related to wiping, a very low fluid level can sometimes trigger an electrical fault. This may not be the primary cause in your case, but ruling it out will avoid further issues.
Troubleshooting Steps:
1. Check the fuse first. This is the easiest and cheapest fix.
2. Inspect the wiring and connectors. Look for any signs of damage, corrosion, or loose connections.
3. Test the switch. See if you can find a continuity tester to check the switch, or see if the problem seems to be associated with the switch mechanism.
4. Listen for the motor. When you try to activate the wiper, do you hear any clicking or whirring from the motor itself? If not, that points towards a problem upstream of the motor (fuse, switch, wiring).
5. Check the ground. Ensure the ground wire is clean and securely connected.
If you're not comfortable working with car electrics, it's best to take your Expedition to a qualified mechanic for diagnosis and repair. Attempting to fix electrical problems without proper knowledge can be dangerous.
