I fixed it. It was the rear door latch. A few years ago my rear door starting not closing tight no matter how hard or soft I slammed it. Played with the post thinking moving it foward would tighten up the door. Not much adjustment if any there. At that time I didn't have a door open light staying on. That came later. When it did I was able to play around with different closing techniques to extinguish the light. Then no matter what I did no bueno. After reading all the posts decided it's got to be the latch. I took the rear door panels off to get a better look. This is a PITA. Can skip. See end of post. Removed the three bolts holding the latch on. Saw the wire coming from the latch. It's actually two wires in a sheath. It terminates as a plug which facilitates the easy removal of the latch. Unplugging turns off the light. Don't have to cut any wires. This is one solution. I then inspected the latch. The piece that engages the post in the latch housing can be manually closed and then manually opened by pulling on the cable. I was able to turn the light off and on by doing this simulating a door closed and door open condition. So why isn't the light going out normally? The latch part in the housing that pivots approximately 90 degrees was pivoting less than the full amount causing the door not to fully close, yes close and lock but not tightly. And the door ajar sensor in the housing was only partially activated. The latch can not be taken apart and reassembled unfortunately. Two rivet like bolts hold everything together. Upon closer inspection I saw the problem. The latch part that pivots on the left rivet was originally coated in plastic. That plastic coating, due to corrosion and years of exposure, had come loose. While most of the plastic was missing there were bits and pieces present that were preventing the pivot latch from fully pivoting 90 degrees. I removed as much of the plastic as possible, sprayed the inside of the housing with wd40 and reassembled everything. No more light and a nice tight fit when the door is closed. A new latch will cost you $130 if this doesn't free up the latch. Long story short. Don't have to take the panels off. Just open the door and dig out the little pieces of plastic in the latch, if any, spray wd40 in the latch. If you are good don't even have to remove the three latch mounting bolts. Oh and don't over tighten the bolts. I did and snapped one.
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