There are 2 black "nubs" in the center defrost vent. Not sure what they do?Yes, typically found on the top of the dashboard
Light switch set to automatic?
Did you ever figure out the problem? I have a 2007 Suburban that does the same thing.My dash lights aren't working. They used to come on automatically when getting dark. I've checked the fuse on the drivers side dash.
Is there a sensor that turns the light on when the sun goes down?