I lost my interior lights last night sometime on my 2001 3.8. It's really strange, when I turn my car on (at night) the PRND321 lights are fully illuminated but when I release the emergency brake, the headlights come on and the gauge cluster lights SHOULD come on along with the steering wheel, hvac, etc. In addition, the PRND321 dims almost down to nothing, but doesn't go completely out. The turn signal indicator light, high beam indicator, and message center still all come on too. I was thinking either a fuse or the dimmer switch needs replaced but I don't want to replace the dimmer switch unless I am sure that's the issue. The manual adjustment between low and high beam still functions on the dimmer switch, just turning the **** does nothing. Has anyone run into the problem before and what was the culprit?

 

Sounds like it could be a problem with the instrument panel dimming switch in the headlamp switch. The I/P dimming switch varies the voltage level to the to the interior lights, dimming them or brightening them accordingly through the I/P dimming switch circuit. Could also be a bad ground for that circuit.
Could also be an ambient light sensor issue. They can cause various illumination problems when they or the wiring to them go bad. Try cleaning the lens first. It's the small bulb on top of the dash, just left of center.

Here's a link to a thread from another forum about a similar issue: Interior Auto Dimming

 

Turns out I also dont have tail lights but I still have turn signals and brake lights. I replaced the dimmer switch with one from a junkyard and had the same symptoms. I suppose the switch from the junkyard could have also been faulty. I checked fuses and they all looked good. I cant decide if I should look for a short or buy a brand new switch and try again.

 

Possible, but I don't think they fail very often. I think I'd lean toward the ambient light sensor.

 

I cleaned the ambient light sensor, still no change. Not sure what else to do at this point. I've heard it could be the BCM.

This may not be relevant, but I did plug in an OBD II scanner to my car when my lights still worked, then after I plugged it in, later that night is when I noticed the lights weren't working. I wouldn't think that would cause any problems, but who knows at this point.

 

I have a bit of an update: I found that the 15 amp tail light fuse on the passener side panel was blown, I replaced the dimmer switch on the dash with one from a wrecking yard and it still blows it out every time. Not sure what else to look for at this point.

 

Clearly a short someplace, either to ground or open. I would start by checking tail light grounds, but it could be anywhere in the circuit.