System Description

Voltage is present at the Main Light Switch at all times.

Radio LCD Display Illumination

With the Ignition Switch in ACC or RUN, battery voltage is present at pin 5 of the LCD Dimming Relay through Fuse 6. With the Main Light Switch in OFF, the Relay is NOT energized. With these two conditions present, full battery voltage is applied at pin 5, connector C257, of the Radio. The LCD Display illuminates at full brightness for maximum daytime visibility.

If the Main Light Switch is placed in PARK or HEAD, the LCD Dimming Relay is energized. The voltage at pin 5, connector C257, of the Radio now depends on the Dimming Rheostat portion of the Main Light Switch. With the Main Light Switch knob twisted fully counterclockwise, voltage on circuit 19 (LB/R) is high and the LCD Display is brightly illuminated. As the knob is twisted clockwise, voltage on circuit 19 (LB/R) drops and the LCD Display dims.

Digital Cluster Illumination

With the Main Light Switch in OFF, no voltage is applied to pin 29, connector C255, of the Digital Instrument Cluster. This input prompt the Cluster to illuminate at full brightness for maximum daytime visibility.

With the Main Light Switch in PARK or HEAD, voltage is applied to pin 29, connector C255, of the Cluster through circuit 19 (LB/R). With the Main Light Switch knob twisted fully counterclockwise, voltage on circuit 19 (LB/R) is high. The Digital Cluster circuitry uses this as an input to illuminate brightly. As the Main Light Switch knob is twisted clockwise, voltage on circuit 19 (LB/R) drops and the Cluster circuitry causes display brightness to decrease.

Clock

With the Main Light Switch in OFF, no voltage is applied to the Clock on circuit 14 (BR). This input prompts the Clock to illuminate at full brightness for maximum daytime visibility.

With the Main Light Switch in PARK or HEAD, battery voltage is applied to the Clock circuit 14 (BR). The Clock uses this as an input to dim.

All Other Illumination Bulbs

All other instrument illumination bulbs are fed by circuit 19 (LB/R) from the Dimming Rheostat portion of the Main Light Switch. With the main Light Switch i PARK or HEAD, and the knob twisted fully counterclockwise, voltage on circuit 19 (LB/R) is high and all illumination bulbs burn brightly. As the Main Light Switch knob is twisted clockwise, voltage on circuit 19 (LB/R) drops and all illumination bulbs dim.