Lets see who can solve this perplexing mystery.....bet it will make you scratch your head a bit:

Patient: 1994 Mitsi Montero LS, 5 speed, 3.0
Ailment: Dern "Door Ajar Warning Light" always stays on

All 4 doors have a simple push switch that will send a signal to the dash "Door Ajar" light if the door is not fully closed. There is also a switch on the rear cargo door, but for some reason the Mitsu engineers went with a more complex (and hard to get to) switch that is part of the door latch mechanism, up behind the door handle. Since it is much harder to get to, I assumed that it was most likely the rear cargo door switch that was bad......so, I attacked that one first:

I removed the lower door panel, and peeled back the plastic to get as close as I could to the door ajar switch. I located the wire feeding the switch, and pulled it apart to check continuity with a meter. With the door "open", there was continuity between the wires, so it would be telling the "Door Ajar" light to be "on". I then used a screwdriver to put the latch in the closed position, and checked continuity.....this time there was no continuity and thus the Door Ajar light would be "off", as it should. So the rear door switch tested fine.






I then went to each of the 4 doors and pulled the switches off and tested continuity:







You can just put one test lead on that flat metal part of the switch (or right into that screw hole for ease of holding), and the other lead on the prong inside the female end of the switch.......then just push the switch button in/out to make sure there is continuity only when the button is out and no continuity when the button is pushed in.

In my case, all the switches were fine. Even with all 5 doors with the switch/wire lead disconnected, the darn "Door Ajar" light in the dash was still on. So, I am thinking "is there another switch someplace else?" I went ahead and looked under the engine hood for a switch, but found nothing......and the light stayed on with the hood open or closed. So, I hooked all the door switches back up, and plugged up the rear door wire connector, shut all the doors and looked at the dash.......the "Door Ajar" light was still on.

Pretty crazy. Does anyone have a logical explanation as to why the Door Ajar light stays on, even with all the switches in good shape?

I had pulled out enough hair on this one, so I started playing with the fuses to try to find the one that covered the Door Ajar light system. I found it pretty quick: Its the "Clock/Room" fuse.......upper right-hand corner in pic:




So, I just pulled the fuse and will keep it out until I figure out what the real problem is. Maybe someone has some good suggestions?

 

Do the dome lights inside come on at all as well? I would think for some reason the door is not pressing on one of the switches enough to open the circuit.

 

The fact that the Door Adjar light stays on while all switches are disconnected makes me think that a wire(a) going to one of those switches has worn out insulation somewhere and is touching bare metal of the door or vehicle body. This provides ground to the circuit and is indistinguishable from an "open door" signal via a door switch. The age of the patient makes this a likely ailment. I'd start by checking the wires in the driver's door. Especially at the point where they go from the door to the body.

 

Ah didn't think of that, nice suggestion.

 

Hunter........Last night that thought came to me also, that maybe one of the wires had worn against the body metal someplace and was grounding out. Good to hear that you thought of that also, so now its just a matter of "trying" to find that short. Good idea suggesting the drivers door area as that is the most worn over the years. However, the wire does not run inside the door, but down under the rocker panels......might be a beast to try to find.

Now if the wire was grounding out someplace, would that make the fuse blow? Fuse was not blown. And like Naeos suggested about the dome lights........the map lights were working, but that larger dome light was not working.

Naeos......I checked where the door body was pressing against the switches, and all is good. No rubber bumpers are used, and there is no rust or door damage. I even tried pushing on the switches to see if the light went off, but to no affect.

 

Since the current is going through the dome light (load) to ground via switch or via short, the short in this particular case will not blow the fuse. It will simply mimic the switch being activated. Since the wire is running inside the body, that makes it a little more complicated to trace. Without having a wiring diagram, I'd do the following:
1. Open the dome light and figure out how it works. Does it have a single wire going to it? If so, then the power to dome light is going via some relay, because you have 12 v. coming in and the light is grounded. That means that computer gets signal from door switches and then controls the dome light. In that case, proceed to step 3?
2. If dome light has two wires coming and going, then find the wire that is ground and connect Ohmmeter to it. Connect the other end of meter to the wire that you disconnected from door switch. Do you have continuity? Wiggle the wire inside door frame and see if it will connect/disconnect continuity at any point.
3. If dome light is controlled by a separate circuit, you need to find the end of the wire from the door switch (ether under the instrument cluster or at the computer or relay and do the same continuity test. It will help if you have electrical diagram, so that you can figure out where connections are and what color wires to trace.

One more thought - have you tried to short the contacts coming from the door to see if that will turn off the light?

 

Did some more tinkering on the "Mystery of the Door Ajar Light" issue:

Pulled back the driver's side rocker cover:
You can see the big bundle of wiring running just under these plastic panels, and easy to get to. In the pic you can see the door ajar switch in the lower right corner, and its opposite to the support pillar. So, I peeled off the inside plastic that covers the seat belt assembly:







Underneath the seat belt 17mm bolt's washer I found a grey wire totally smashed by the last gypsie who installed that seat belt assembly: The copper wire was exposed and grounding out on the bolt's washer. I just cut out the bad spot and and re-spliced the wire.



That solved the problem. The Dome light is now working as it should, and the Door Ajar Light now goes off when the doors are shut, and comes on when open or if they are not shut all the way. So, that solved that bizarre mystery........on to the next issue.

Hunter........thanks Doc for the detailed advice on tracking down the bad wire. You were totally right with your diagnosis of this ill patient, and your surgical instructions were the only way to operate.

One curiosity: This grey wire that was "smashed" by the seatbelt bolt was actually spliced/soldered into one of the green door switch wires (not factory). This grey wire then runs under the passenger door rocker cover and toward the back. I did not trace it down, but Im guessing it is part of an aftermarket alarm system. Anyone have any idea of what else it could be fore?