These were usually an open resistor board inside the dimmer switch on the dash for the interior lights. This switch dims the dash lights and will turn on the interior lights. If you've checked all the fuses, pull the switch out to access the connector. Turn the headlights on and test for power to and through to the dash lights. If you have power to the switch and nothing out to the dash, you've found your problem. If there is power through the switch to the dash, you've got a problem farther down the circuit path and will need further chasing. Like I said, it's usually the switch but check first.
