Last evening when I shut down, no interior lights. Just the instrument cluster. I tried the instrument dimmer ****, no lights. I tried the push buttons next to the overhead lights, still nothing. All fuses are good.

Any ideas?

Thanks.

did you check both fuse boxes? under the hood and under the seat? May be a stupid question to ask, but that happened to me one time when I first got the car, and I didn't realize I had 2 fuse boxes.

Was it dark when this happened? If the light sensor senses daylight, the interior lights will not come on.

I thought of this but the twilight sentinel turns on the headlights and instrument panel lights. I suppose it is possible I mistook the DRLs for headlights, but the instrument panel lights wouldn't be on would they?

Plus, even with the sensor sensing daytime, wouldn't the manual buttons still work?

Yes, Thanks phoenix. It took me a while, but I noticed there were two.

Do you hear a click from the rear fuse block when you try and turn them on? I would check the relay "INT LP" which is responsible for providing power to this circuit. You may also have a bad ground somewhere. Failing this, the news may not be good. Interior lamp control, including dimming is controllled by the rear integration module. This would be where I would check next if everything else has been ruled out.

After further investigation, I did find a blown fuse and replaced it. But still nothing!!?? I hear a click from the relay you mention so I interpret that to mean the RIM is working well enough to turn on the relay. I am at a loss about what "event" caused the fuse to go.

I will check the relay - just because it clicks doesn't mean it works.

Also, I don't know what or how things are supposed to operate given that the sensor now says it'* daylight. I would think that I should be able to override what it wants to do by using the manual switches. :?

You can override them. Even if the dimming circuit isn't working, the way things are wired you should still have on/off by command of the Twighlight Sentinel. I'd carry on with further checks of the relay, then start looking for grounding problems.

Thanks Darcy, I'm on the same page with you. I suppose I'm secretly hoping it'* the relay (it has moving parts). Logically, I don't get why the grounding would change. But if there is corrosion somewhere, I guess it has to fail sometime.

We'll see...

I would agree. Unless you've had some serious water problems, the corrosion is unlikely. GM did a pretty reasonable job of placing the grounding splicepacks in the 2000+ vehicles to avoid this.