It might also be a bad ground with the cd player. I had a 91 firebird just like yours, and that happened to me too. Very carefully check the wires to and from the radio, make sure your diimer switch is at the brightest setting ( I know it sounds dumb, but it's sometimes the most overlooked thing when it comes to the dash lights) and also check that all your brake lights work. If a bulb is out in the back, the dash lights go out to indicate the driver. good luck!