In many vehicles, the dash lights are on the same circuit as the tail lights. Are these instrument lights working? If not, then there is a problem in this circuit. If the intrument panel lights work and are not on the same circuit as the tail lights, do you have a connection for trailer lights? If so, you might check to see if this is somehow causing your problem.
The tail lights should also go on with the parking lights. If the parking lights are not working, the switch might be a suspect.