ok.. here is a little more info... I can get more detailed later...
dimmer circuit operation.
During normal operation, the Instrument Panel Dimming Rheostat controls a small number of lamps on the 88 (BK/W) circuit. Most dimmable lamps are fed through the Pulse Width Dimming Module, which duplicates the illumination level of the rheostat at a higher power output.
Certain lamps must be illuminated fully during the daytime and dimmed at night(484 [O/BK] circuits). This is accomplished by a switch in the Main Light Switch (in vehicles without Automatic Headlamps) or by the LCD Dimming Relay (in vehicles with the Automatic Headlamps).
Do you have autoheadlights or not? there is a little difference in the circuits.
The dimmer control and PWM are kinda wired in parallel.. right now, I am betting that you have bad PWM, or wiring problem. PWM is not used when parking lights and headlights are off.
There is also a LCD dimming relay in this circuit if you have autolamp. This controls ONLY a couple items, thats why it is important to know about all the dimmable lights in car, to see what ones work or not. The LCD dimming relay only effects the instrument panel, digital clock (seperate from radio), and radio illumination.
Also, check fuses 13, 15, 6...