Re: "Door ajar" and interior lite malfunction?
My issue was that my cab doors were not closed all the way, they were able to wiggle and therefore make the "door ajar" light and, occasionally, the dome light come on as well. I sprayed the hinges and jaws on the cab doors and driver's and passenger door with WD-40, and make sure I shut my doors tight now, no problems. Others will tell you to spray some WD-40 into the jaws as well, and on the mechanism that tells the dome light come on, and maybe adjust your locking jaws as well.
2001 Ford Ranger XLT Stepside: Stock