"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?

Asked by for the 2002 Ford Expedition
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?
2 more answers
Usually its the drivers door because it's opened twice as often as the others
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