Hi all, long time reader, not much of a poster but i hope someone here can point me in the right direction.
My 2003 MC SS has an annoying issue that has bugged me for a while now. I just bought this car a year ago and its a fine car other than none of the interior lights will work.
By this i am referring to the dome lamp in the headliner, the little 194 lamps at the foot well on either side, or the two map lights in the rear view mirror.
The cluster lights and everything else about the car works as should just fine. I have checked the bulbs, the trunk/roof/brp fuse is good. however with a test light i get no current to that fuse. Yes i have changed the fuse anyhow and verified as good with another same amp fuse.

The onstar mirror power button lights up if depressed, the overhead information with outside temp and compass works fine. If i leave the key in the ignition and door open, i get the chime so that door switch is working as should.

I have searched the forum here and a couple other threads with the same issue popped up and 1 said he fixed the problem but never elaborated on how or what the cause was.
I would thing if it were a bcm issue i would have other funky issues than just no interior lamps, but i could be wrong. If anyone can point me in the right direction i would be much appreciative and dance at your next wedding

 

OK so if the fuse isn't getting power the wiring diagram would seem to show that maybe the battery run down protection relay is faulty since the DIC is working and the DIC/RKE fuse should be good then. Also have you had the battery checked?
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Hi AAron, no i havent actually tested the battery myself. It looks like its new, and never had any starting problems and altternator charges just fine. didnt know the battery run down relay was tied in with those lamps.
I will give it a check tomorrow

 

Have you checked the dimmer control on the light switch to make sure it is turned up? I'm thinking the light switch may be bad since that is what the ground circuit for the interior lighting runs through.

 

I have tried turning the headlight switch all the way to manually turn the interior lights on but all it does is brighten and dim the cluster and radio lights. Will not activate dome or floor lights.

 

On the 2003 wiring diagram I've got some of the affected lamps, like the footwell lamps, run into the BCM and then the BCM does have a line which goes out to the dimmer switch and then ground. (yay for ground side switching)

If the ground was bad I think OPs test light would be lighting up at least on one side of the fuse even if the fuse was bad. OP said the test light was not lighting on the fuses at all which either would mean user error or the fuse is getting no power which is why I looked into the battery run down protection relay.

The OP could swap that relay with the parking light or backup lamp relay temporarily I believe they're the same relay and all located in the passenger side fuse panel.

 

Good news Aaron, its the relay you mentioned.
Funny thing is, there was no relay in the slot at all. I noticed that when i was checking the fuses, that there was a empty slot where that relay goes. I just now pulled the relay beside where it should be, plugged it in and all the interior lamps worked. Foot well,dome and map lights came on and after shut the door about 30 seconds they went off.
No idea why someone removed the relay in the first place.
So i put the relay back where it came from and will get a new one and install it.
thanks for help a ton, i appreciate it

Im no master mechanic by any means. i have worked on cars my whole life, but mostly the nuts and bolts side. this electircal stuff throws me for a loop. wouldnt have firgured it out without ya.
if you happen to be a nascar fan, give me a pm and ill hook you up with pit passes next time a race is close by.

 

Wonderful I'm glad that you got that all figured out and that it's an inexpensive fix!
Previous owners do sometimes silly things to vehicles. The only reasons I could see removing that relay is; if one of the other relays went out so they "borrowed" it to have the other systems working and never got around to replacing it, it went bad and they never got around to replacing it, or they had a parasitic draw issue with the battery draining and removed the relay to "fix" that.

I'm ok with turning a wrench but I actually prefer electrical circuits and wiring diagrams so we're pretty close to opposites I can solder and own a hot air reworking station for working on surface mount electronics. There's lots of mechanical things I've never done to a car which others here have vastly more experience than me doing.

This pdf copy of the 2000-2005 monte carlo factory service manual I bought online is really quite useful for some stuff like this