I have an 2001 DS. Everyonce and awhile while driving the door ajar light will come on and the little bell will chime. It will stay on for a few minutes or even until I get to my destination and shut the truck off. Or sometimes when I start the vehicle the interior light will stay on with the door ajar light.
Since it’s basically a Ford Ranger, the light switch is built into the door latch.
My wife’s 98 Windstar used to do this occasionally. The fix was to spray CRC Electrical Contact Cleaner into the door latch while working the door handle to clean the switch electrical contacts. I’ve used WD-40 in a pinch, but prefer the CRC.
Ed is right. I keep the CRC product on hand just for Ford products with this issue. I like to hold the latch open with the outside handle and work the latch itself open and closed with the 1/4" shaft of a screwdriver SEVERAL times. I have not had one that wasn’t fixed by doing that yet.
I use PB Blaster for this problem, it does a god job.