So I've had this problem for awhile now but never could find out how to fix it. I've searched and still haven't found how to fix it. I believe it all started when I was installing my after market radio. Dimmer switch is fine, i got like 5 from the junk yard so atleast one of those should have worked haha. I've checked fuses like 3 times each and they all seem fine. Only thing I can think of is a shorted wire or I heard people say it could be the BCM.

1999 Pontiac Sunfire GT

When I installed a aftermarket radio in my Sunbird and I had the same problem. I used an adapter rather than cut the factory plug and it turns out two of the wires on the adapter had to be connected to each other they were wires that had to do with the factory display dimming when you turn on the headlights once I connected the two the dash lights starting working again.

There's a small gray wire that goes to the radio (that controls the interior lighting, but also connects to the radio for illumination). If you didn't connect it properly, it will prevent the rest of the lights from working.

The first time I did a radio... which was a looooooooooooong time ago... I accidentally used the gray wire for a speaker connection (in my defence.. there are two gray wires). Didn't work properly, obviously.