1. Check the door lock actuator:
- Using a flat-head screwdriver or other prying tool, remove the door panel to gain access to the inside of the door.
- Once the panel is removed, you will see the door lock actuator.
- Inspect the actuator for any damage, such as loose wires or broken gears.
- If necessary, replace the actuator with a new one.
2. Check the door lock linkage:
- Check if there is anything obstructing the door lock linkage such as broken pieces of the plastic door handle or the metal rods.
- Check if any part of the linkage is damaged or disconnected.
- If any part is damaged, replace it accordingly.
3. Check the child safety lock:
- Make sure the child safety lock is not engaged.
- If it is, disengage it by sliding the switch to the "unlocked" position.
4. Try unlocking the door manually:
- Use a key to unlock the door from the outside.
- If the key turns but does not unlock the door, the lock cylinder may need to be replaced.
5. Lubricate:
- Make sure all moving parts are properly lubricated. Use a dry teflon or white lithium grease to apply to all moving parts.
Once you have completed all these steps, the door of your 1991 Grand Marquis should be unlocked. If you are still experiencing issues, you may need to take your vehicle to a mechanic for further diagnosis and repair.
