Door ajar light stays on but all the doors apear to be shut?? 2003 Windstar

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.

it means one of your doors are not shut could be back door if all doors are shut theres sensors on frame of doors

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

Spray lubricant in the driver's and passenger door latches. One of the switches in the latch are sticking. Open and close the door several times to free up the switch.

the little bottons on the inside of one of your doors needs to be taken off and cleaned

to repair this problem you must remove floor lights from seats and check the circuit for either a short or a stuck switch use a multi tester this can get to be irritating as the short may be not directly behind switch could be along wiring that runs through car my suggestion if your not electrically proficient is take it to an electromechanic shop or simply unplug the light from socket to avoid draining the battery.

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.

sounds like door switch is bad

Remove "Door Ajar" switch. Clean the switch and use a graphite type lubricant (I recommend "Dry-Slide") to lubricate the actuator on the switch. Reassemble the switch.

The switches are located inside the door panels, attached to the catch mechanism.

1) Remove interior door panel.

2) Using a T-27 Torx driver, remove the 3 bolts holding the catch in the door.
2a) The door ajar switch is the only part on the mechanism with the 2-wire harness.
2b) The switch is located at the rear catch for the sliding door.

3) Using a small flat screwdriver, gently lift the black tab on the catch mechanism and rotate the switch to remove it from the catch assembly.

4) Using a rag, clean the small round actuator and apply a small amount of graphite lubricant to the actuator and work the switch so it moves freely.

5) Reassemble the catch and the door.