GM Service Manual Online
For 1990-2009 cars only

Circuit Operation

The I/P dimmer switch controls the brightness of the following:

    • The incandescent illumination lamps of the instrument cluster
    • The vacuum fluorescent  (VF) displays of the radio

Incandescent Dimming

When the headlamp switch is in the PARK or HEAD position or in a low light condition with DRL active, voltage is applied through circuit  9 to the I/P dimmer switch. Voltage from the I/P dimmer switch is applied through circuit  44, the I/P dimmer fuse and circuit 8 to the incandescent lamps. Turning the I/P dimmer switch changes the voltage on circuit  8. The changing voltage varies the intensity of the lamps.

Vacuum Fluorescent Dimming

When the headlamp switch is in the PARK or HEAD position or in a low light condition with DRL active, voltage is applied through circuit  9 to the I/P dimmer switch. Voltage from the I/P dimmer switch is applied through circuit  44, the I/P dimmer fuse and circuit 8 to the radio VF display. The radio VF display dims for night viewing. Turning the I/P dimmer switch changes the voltage on circuit  8. The changing voltage varies the intensity of the radio VF display.