What year is your car, and what model? Wiring varies. In the later models at least the instrument lights are controlled by a rheostat on the light switch which can be turned to adjust the brightness. This pot could have been turned all the way down, or there could be a bad spot on the stat or it could be broken, rusted, etc. If it is defective, lights can be restored by shorting out the rheostat, but then they will always be on bright. If your year is so equipped, turning the light knob back and forth will give you some info on what is going on.