* Switch itself: The switch might be internally broken. This is often the case, especially with the driver's side switch which gets the most use. The solution is to replace the switch. These are relatively inexpensive and can be found online or at auto parts stores. Replacing it can be a DIY job for someone comfortable working on car interiors, but it requires some disassembly of the door panel.
* Wiring: A broken wire within the door harness is also possible. This is often caused by the repeated flexing of the wires as the door opens and closes. Troubleshooting this requires tracing the wiring from the switch to the window motor. A multimeter is helpful for this task. Repair might involve splicing in new wire or replacing a section of the harness.
* Window motor: Less likely, but possible, the window motor itself could be the problem, and it's not the switch at all. A faulty motor could manifest as a seemingly bad switch. You'd need to check the motor's operation independently to rule this out.
* Fuse/Circuit Breaker: Before diving into switch or wiring repairs, check the relevant fuse or circuit breaker in the car's fuse box. A blown fuse is a much simpler and cheaper fix.
To diagnose:
1. Check the fuses: This is the absolute first step.
2. Try other windows: Do other windows work correctly? If so, it points to a problem localized to the faulty window's switch or wiring.
3. Test the switch (if possible): If you have some electrical testing skills, you can check for continuity through the switch with a multimeter. (Caution: disconnect the battery negative terminal first!)
4. Visual inspection: Carefully inspect the wiring harness inside the door for any obvious damage or disconnections.
To fix:
Replacing the switch is generally the most likely solution and usually the easiest. YouTube videos demonstrating the door panel removal and switch replacement for a 2003 Lincoln Town Car are a valuable resource. If you're not comfortable doing this yourself, a qualified mechanic can perform the repair.
