The MIRROR (Pontiac) or RDO/INT (Chevrolet) fuse in the IP junction block supplies battery positive voltage to the body control module (BCM). The inadvertent power control circuit of the BCM supplies battery positive voltage to the IP junction block. The IP junction block supplies battery positive voltage to the left and right hand courtesy lamps and the dome lamp. When any door is opened, the door jam switch contacts close and the door open input to the BCM is grounded. The BCM provides a pulse width modulated ground to the left and right hand courtesy lamps and the dome lamp for the theater dimming feature.

The IP junction block also supplies battery positive voltage to each reading lamp and the rear compartment (trunk) lamp. When their switches are closed to provide ground, the lamps will illuminate.

The dome lamp switch has three positions, DOOR, OFF and ON. When in the DOOR position, the dome lamp operation is controlled by the BCM. The ON position provides a ground for continuous operation. The OFF position turns off any dome lamp operation.

If the driver inadvertently leaves any interior lamp on, the BCM will turn it off in 18-22 minutes.

The BCM supplies voltage to the instrument panel dimming lamps when it receives a parklamp-on signal from the parklamp switch. The intensity of the lamps is controlled by the instrument panel lamp dimmer switch and the BCM. The BCM provides voltage to the dimmer switch and a signal return (ground). The instrument panel lamp dimmer switch consists of an internal potentiometer which varies the voltage to the BCM depending on the position of the dimmer wheel. The BCM uses this signal to control the intensity of the lamps by providing a pulse width modulated (PWM) signal to the lamps. When the BCM senses a minimum input voltage, it provides a maximum duty cycle signal to the lamps and vice-versa. Ground for the lamps is provided by the individual components.