What would cause the dash lights on a 1999 Tahoe to not turn on?

odds are all the dash are not all burned out (usually little 194bulbs). I would check the Headlight switch itself (uming this has the combined Headlight switch/rotary dimmer). If it has a separate dimmer switch then you will want to check that it is getting feed. I wouldnt go tearing my dash apart just yet, as atleast some of the bulbs are still good.