I'm having an issue with my interior lights not coming on when a door is opened. When the switch in the light fixture above the rear view mirror is in position 1 (ON) they all come on so I know they all work. In positions 2 and 3, nothing happens. After going through the lock/unlock with the fob a bunch of times, as well as with the key in the driver's door, suddenly I noticed position 2 was turning on the interior lights. The trouble now was that they wouldn't turn off unless I manually slid the switch to the bottom (OFF). I slid it back to position 2 and after about 10 minutes they were off again, and once again only position 1 would make them come on.

My rear door is mis-adjusted and doesn't close properly, in fact it kind of looks like it doesn't even close all the way along the top because the upper left corner has a 3/8" gap between the door and the gasket but it is latched tight at the handle. I suspect the BCU is interpreting this as a door being open and when I cycled the locks/alarm I reset something. Then after 10 minutes the BCU shut down the lights again. I presume this is the intended function of the timeout that preserves your battery if you leave a door open. I read in another post that some have found that it takes a while for the BCU to start operating the interior lights properly again once that happens.

My question is how does the BCU know any of the doors are open? I can't find any of the old-fashioned plunger switches anywhere so there's obviously a more sophisticated system at work. I'm going to swap the rear door from my other truck, only because it has the ladder and a few stickers on it that I like, and hopefully I can do a better job than the PO did aligning the current door. Is there any way to determine if the BCU thinks the rear door is open all the time? It kind of sounds like I've already done that from the behavior of the lights, but I'd like to confirm if someone can clue me in on how this thing works. The only other thing of note is that I already swapped the driver's door from my other truck (along with the cluster, ignition switch, BCU, and every other computer) so maybe that door is the offender somehow. I have to suspect the rear door first though since it's not closing correctly.

 

Rent the Nanocom to see what doors are thought to be "open" by the BCU.

 

I haven’t fired the engine since I swapped the driveline over from the 04. I replaced the headgaskets in the process and tried to use as many of the 04’s parts as possible when doing the swap. The 04 was was code-free before I started doing the work and hopefully the 03 will “wake up” in the same condition however I suspect a Nanocom will be in my future.

Thanks for the suggestion, I’ll back burner this problem and move on. If and when the time comes to get a Nanocom I’ll address it then, that’s a good idea.