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Interior lights staying on

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digitalgpbandit

New member
I have an on going issue over the past couple years with my '99 Grand Prix. Basically one day I was driving into work and the interior dome lights randomly popped on and didn't go out. Obviously the first thing I checked was the dimmer switch. I shut it off all the way and the lights were still on. When I got to work I shut the car off took the key out, re-inserted and turned to accessory. Lights stayed on. Locked the car with the remote. Lights stayed on. Basically they would stay on until the battery saver thing kicked them off. Once I unlocked the car the same issue would happen all over again. So I ended up pulling the courtesy light fuse and left it with no dome lights at all.

So here is where the fun begins. I replaced the dimmer switch & then the BCM being told with certainty by multiple sources including a couple professional mechanics. Neither did anything to resolve the issue. I am equipped with the digital DIC and that properly shows the doors being opened and closed. I was told there are two door switches on these cars, one for the DIC and the other for the lights. Supposedly the door switches are integrated with the door lock actuator and need a tech II to figure out which one is grounding out the light circuit causing them to go stay on. I was able to track down an old work acquaintance from a GM dealer I worked at years ago. He's still with GM and says he's never seen that issue. I met him on his lunch break one day last year to scan the car with the Tech II. No codes came up at all and everything appears to be functioning properly from what its picking up. I've done some google searches and see that there are a couple others having the same issue with their Grand Prix, but never saw any resolution posted.

Anyone else have this issue with the dome lights staying on & has anyone come across a real solution for it (beside pulling the fuse)?
 


A faulty door switch can do the same... Just sayin ;)

All in all, electrical problems are always the worst to troubleshoot and resolve.
 
That's pretty much where I am at. Trying to find a pinched/shorted wire or figuring out which door lock actuator to replace since there is no actual door switch. I guess one of those trial and error things. I did happen to notice the plastic wire loom that goes into the trunk lid just kinda dangles there. I'm wondering if it's for the trunk light switch and if that would have anything to do with my issue
 
This isn't really that tough. Do you have a multimeter? Are you comfortable using it in diode mode (aka the one where it beeps if you touch the leads together)?

These cars have a connector at each door, pull the car side of the boot and you can get to it.


With a mulitmeter and a wiring schematic you can rather quickly test if the wire is sending back a ground signal to the bcm. If it's not there.. then like Brandon said you pull all your bulbs and test there with a multimeter. Presto, quickest way to find the problem.
 


No go on the multimeter so far, but I did take the door panel apart. I found something interesting...a blue plastic cylinder shaped thing and a spring laying inside the door well. Anybody have any clue where this goes to? I'm wondering if that has anything to do with my issue.
image_1.jpeg
 
Bringing back an old thread. I can breath a sigh of relief that this issue I've been having for about the last 4 or 5 years is finally resolved! Turns out it was the switch on the trunk latch all along. Weird thing is that the indicator on the DIC always functioned properly. Guessing there must be two separate switches like in the doors
 
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