Dimmer Switch: Description and Operation

The Light Switch controls the brightness of the incandescent lamps and Vacuum Fluorescent (VF) displays. The incandescent lamps are located in various components (see schematics) and the VF displays are located in the Radio, and Instrument Cluster.
The brightness of the incandescent lamps is determined by a variable voltage signal produced by the Light Switch.
The VF display's brightness is controlled by two signals: the dim display signal and the VF display dimming signal. The dim display signal signals the VF displays that the Headlights or Park Lights are OK. When the dim display signal is not present (Headlights and Park Lights OFF) the VF displays are fixed at high brightness for easy daytime viewing. When the dim display signal is present, the VF displays will dim. Their brightness can be adjusted by the Interior Lights Dimmer Switch. In this mode the displays respond to the VF display dimming signal. This is a Pulse Width Modulated (PWM) Signal. The PWM signal consists of a series of pulses. The width of the pulse determines display brightness. The pulses are widest at full brightness.
In the daytime, if the Headlights or Park Lights are ON, the VF displays will dim making them difficult to read. If the Dimmer Switch is placed in either "PARADE" or "DOME" this will override the Lights ON Input and the VF displays will remain at full brightness.
With any door open or with the Light Switch in the "DOME" position, terminal "C" of the Light Switch receives a ground signal from the Door Jamb Switch through the WHT (156) wires or internally through the Light Switch. When the last door is closed and the Light Switch is not in the "DOME" position, or when the the Light Switch is moved from the "DOME" position with all doors closed, ground is removed from terminal "C" of the Light Switch. The Light Switch then supplies voltage for about 30 seconds through the GRY (8) wires to illuminate the various components.