2003 Mercury Grand Marquis

Sounds like the door is not lined up correctly so it's not closing all the way. Double check your work and adjust the door. Hope that helps! Jim

I changed all 4 doors. How do I determine which door is not lined up?

One at a time, with the other 3 doors closed, push the dome light switch button in by hand. It should be a little push button on the door jamb. When the dome light goes off, you've found the offending door. Does the door ajar warning light on the dash stay on too? It looks like a little red bug. At least to me that's what it looks like. Hope that helps! Jim

Possible bad door latch. I believe the switches are integrated into the latch.

Is there a way to short the latch to make the system think the doors are closed ok? Then I may be able to check the doors one at a time.

Take the wires that go to the latch and try wiring them directly together. I can't say if the switch is normally open or closed so you may also want to try it with the wires not connected to each other. One or the other should fool the system into thinking the door is closed.