"door ajar" signal is lit on 2002 Ford Expedition

We were driving and the "door ajar" light came on. The doors are all closed. What do we check?

3 answers 1 comment
I see Dorman/Help has door jamb switches available for about $13, So call your local parts stores and see if they carry Dorman parts and the labor time to remove and replace this switch is about 3/4 of an hour
How do we find out which door it is?
spray the door latches with wd 40 and open and close door a few times to lube also the back gate and window have switchs
Usually its the drivers door because it's opened twice as often as the others