make triple sure the rear door is completely closed. they can look closed, and act closed, and still trip the door ajar switch in the front door w/little movement while driving.
other than that, they are located in the latches. if you open the door and use a screw driver to manually latch the mechanism you will see the button of the switch under the latch arm. some guys lube them, but i find that the lube tends to attract even more dirt over time. i spray them with brake cleaner.
hold the inside handle open, use a screw driver to slip the latch arm back and forth rapidly, and spray brake clean in the hole underneath until the dome light starts workin properly again.
*edit, sheesh i type too slow for this board