1990 instrument panel lights not working

All lights on dash work except those that are connected to dimmer switch, climate controls, and back lighting on gauge cluster. Replaced all bulbs, not the issue (didn't think it was but worth a try). Could it be a bad dimmer switch or would it more likely be a problem in the wiring. How involved is it to get the switch out to replace it? Any suggestions would be great. It's a 1990 camry wagon.