Door ajar light stays on and all doors are closed. What can I do without getting into a big expense

its a bad door ajar switch. which one? you would need a scan tool. but the drivers door does get used more.....

Depending on the make model and year, it could be a sensor in one of the door latches.

You have a bad door ajar switch on one of the doors. It is shorting out and causing the lights to flicker and the door ajar light to stay on.

You will need to spray each door latch including the rear hatch liberally with WD 40 or spray lubricant on the latch and open and close each door several times after spraying. This will usually be sufficient to get the door sensors to detect when you have closed the doors. If this doesn't do it, it will hep to figure out which door is intermittently causing the door ajar light to stay on.

Have lost power to the passenger side door. Without power system doesnt recognize door closed because of no power to door ajar switch which keeps dome light on. Security light stays on because without power to rest of systems supplied by fuse it cannot tell if doors and windows closed to engage security features. Most common is for power wire to break somewhere near where it leaves to main body and enters the door.

go to your local parts store and buy a can of PB BLASTER lubricant then open each door and spray the latch assembley really good then close and open the door 10 to 15 times. do this with each door. the door ajar light switch is located in the door latch assembley and cannot be seen so soak the latch assembleys really good so lube reaches the switch. these switches sometimes get stuck but this usually frees up the switch

The door switch is stuck on or the wire is shorted to ground.

The drivers side door switch goes bad all the time on those, try replacing or check if its sticking.the small little button int the door jam.

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.

you may just need to adjust your door jams they may not be closing properly, the other thing you can try is opening one door at a time and putting your finger on the switch usually in the lower l/h corner of b piller and see if the light goes off if not this may be the problem and replace the switch