I have a 2004 Mercury Mountaineer, V8, AWD, My problem, I think is in the computer? When I shut the engine off and try yo exit and lock the vehicle, setting the factory alarm system it won't do it. The digital display says that there is a "DOOR AJAR". I have checked all the doors as bet I can and they appear closed. BUT the interior lights remain on and the alarm will not set because off the ajar message. Am I missing something? Is the computer having a brain cramp.? I can get the alarm to set if I manually shut off the interior/dash lights too off. then it will work but no interior lights on the dash. This is driving me nuts. Can uou help?Thanks,John

Possibly one of the switch/button contacts on any one of the doors faulty. What I am not sure of is if there is a button on body or the contact is made at the latch on that vehicle

I agree. Sometimes a little wd40 sprayed on switches fixes this issue.

What do I look for in the door jam to spray the WD40 on? I don't see what I am used to as a door switch? Jphn

Spray it up into the door latch mech. Switch should be in there. Open and close doors several times.

Also check the rubber boot where the wires enter the door. Seeing where some owners having issues with wires getting frayed there causing similar issues.

John, did you ever figure this one out? My '04 is doing the same thing. I have to shut off the interior lights in order to set the alarm or use the remote lock. Soooo frustrating! Thanks, James.

I was wondering if you also have a crack in the upper portion of the tailgate? The window portion. The crack has extended from glass to bottom of panel. Is this the cause, thinking that the rear window is open? Also when I turn on the rear defroster the "DOOR AJAR" light also comes on. Still looking for an answer. Anybody out there that can help us??????? John

John, I do have the same crack in the rear door/window but this is common in the mountaineer, navigator and explorer models from similar years. I don't think this is the root cause though. I initially thought maybe I just needed to replace the car battery. I haven't tried that yet. (Thinking maybe not enough power to run the accessories causing this issue.) anyone know if this could be the solution?

John, I hope you didn't give up on your mountaineer. I finally figured out the problem and it cost me less than $10 to fix. It's a broken wire in the boot between the drivers door and the car. Check out this link. Took me 15 minutes to splice the wire. Now it works like a charm!!! http://youtu.be/Vh2r7HrCMRs

Thanks for this help. Mine is doing the exact same thing. Door ajar stays on unless I manually turn all lights off. I also have that crack. Going out on a limb but do either of you have an issue with yours shutting off while driving down the road. Mine used to shoot out spark plugs but think that's fixed. Now I cant drive it because you never know when it will stop its really unsafe.

We had that problem on my boyfriend's car it got so bad when we get in the car all the car would do after starting was click constantly like the doors wanted to lock we did what it said on YouTube and sprayed the crap out of the door locks where they connect to the bar when you shut the door and it's worked and it's never happened again and it's been 3 months

Been there your electric system maybe about to fail check battery and alternator...had the problem for almost a year and finally both went replace both and finally all system go...hope thia works