2003 TAHOE LT 56000 MILES INSIDE LIGHT STAY ON RIGHT REAR DOOR AJ

I have the same problem with my left rear door (it also sets off the alarm at times when parked). I take some wd40 and spray it into the inside lock slide and move it back and forth a few times. that seems to fix it.

One of the door switches is not showing an open contact. Which sugnals the computer that a door is ajar. Try blowunyg comoressed air into every door sqitch including the rear hatch. Afterwards, spray each switch with WD-40. Good Luck.
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It can be issue with faulty sensor or a wiring issue.Troubleshooting is required.
Click the help link shown below:---
Door Ajar Light and Dome Light Remains ON? http://whoisbyme.blogspot.in/2012/06/2003-mercury-sable-door-ajar-light-and.html
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Door ajar light stays on? http://technoanswers.blogspot.com/2012/01/door-ajar-light-stays-on.html

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Thanks.

Check the rear door dome light switch located in the latch assy

The door lock relay or one of the door sensors/ switches is defective.

replace the relay for the courtesy lights. the relay should be under the dash in the fuse panel on the drivers side. if you can't figure out which one. just put your finger on each one till you find the hottest one by touch.

the switch has gone bad in the one of the rear doors. The truck thinks it has a door open, which you know it doesn't.

the wire on the door latch make sure they are plugged in or unplug it and the light should go out if it does not then it's not that door

Try spraying WD-40 into the door latching mechanism (door side). I learned this fix after two battery replacements, but have only had to spray twice in the more than seven years of ownership

I had this problem on my 2003 explorer and took WD40 and gave the lock mechanism a good dose where it meets the clasp on the door jam. Then open and close the doors a couple of times to get them working. They get gummed up and sometimes have a tendency to stick.