What happened to my instrument lights?

I have an '01 Buic Regal LS. About 2 months ago, I suddenly lost the lights behind my instrument cluster. This has an effect on my tripmeter as well making it unreadable. As long as the headlights are OFF,(which is only until you release the parking brake), everything is just fine. When the DRLs come on or you turn the headlights on, there are no cluster lights or tripmeter lighting. I’ve gone through both fuse panels already & checked connections. My next step is to replace the headlight switch. Any other ideas out there?

My guess would be a poor ground to the panel.

I assume you have checked the dimmer control already. I would start the hunt by checking to see if voltage is getting to that first.

Check the dimmer setting. It probably has separate settings for lights on vs. lights off.

I do not know the answer… I found this searching for the answer to my exact same problem on a 1997 Olds Cutlase Supreme… all dash lights work until headlights are turned on… the radio display also goes black… normally the radio display would dim when headlights are turned on… dimmer-wheel is my guess, dimmer wheel still turns on dome light when turned all the way up - clicks into final position and dome light turns on. There is a reostat inside the dimmer wheel which varies the voltage… one contact slides along a resistance wire / path… maybe no contact on reostat? Difficult to test as multi-wire plug controls all circuits.