no head light, tail lights or dash lights
If all three have failed at the same time, I would say that it would be your main switch to turn on your headlights. Not sure what make or year vehicle you have. If it's an older rig, I would say the switch. Most of the new vehicles have relays as well as fuses. Try adding some more information to your problem. You didn't leave much to go on..........make, model, and year will help greatly.