Dash board lights on 2003 Toyota Highlander

Out of the blue, my dashboard lights have gone haywire! When I turn on the headlights, the dashboard lights (including radio dial, clock) turn off. I checked the fuses, and they all seem fine. What could cause this mystery?

Asked by for the 2003 Toyota Highlander
Make sure your dimmer switch isn't turned down? My wife does this all the time.