* Broken or corroded wires: The most common culprit. Wires in older cars can degrade, break, or corrode, especially in areas that experience flexing (like the door jamb). Inspect the wiring harness connecting the door to the car's body. Look for breaks, corrosion, or loose connections, particularly near the rubber bellows where the wires enter the door.
* Faulty passenger window switch: The switch itself may be internally broken, even if it appears fine externally. Replacing this is a relatively inexpensive and easy fix.
* Faulty driver's side master switch: While the passenger window doesn't work, the driver's side master switch controls *all* the windows. A problem within the driver's switch controlling the passenger window circuit is possible.
* Faulty window regulator: While you stated the motor is good, the regulator (the mechanism that moves the window up and down) might have a problem that prevents operation even if the motor runs. This is less likely if neither switch works.
* Blown fuse or relay: While less likely if *neither* switch is working, check the fuse box for any blown fuses related to the power windows. There might also be a relay involved in the system (consult your owner's manual).
* Wiring harness connector problems: The connectors between the door harness and the car's main harness can become corroded or loose over time. Clean the connectors with contact cleaner and ensure a secure connection.
Troubleshooting Steps:
1. Check the fuses: This is the easiest first step.
2. Inspect the wiring: Carefully examine the wiring harness for any visual damage from the passenger switch to the motor and at the door jamb connectors.
3. Test the switches: If possible, try using a multimeter to test the switches for continuity and proper voltage. This requires some electrical knowledge.
4. Try the driver's switch: See if the driver's side switch controls other windows properly. If it has issues with other windows, it is a strong indication the master switch is the issue.
5. Test the passenger window switch separately: If you can remove the switch, test its continuity with a multimeter.
6. Access and test motor directly: If you have the electrical knowledge and tools, bypass the switches and apply power directly to the motor (using the correct voltage and polarity) to confirm the motor is working correctly.
Without hands-on testing, pinpointing the exact cause is difficult. A visual inspection of the wiring and testing of the switches are crucial first steps. If you're not comfortable working with car electronics, it's best to have a qualified mechanic diagnose and repair the issue.
