Interior Lamps Dimming

The Instrument Panel Dimming System operates to provide a variable level of illumination at driver indications and controls. The system works with both incandescent lamps and with vacuum fluorescent displays as in the PRNDL display at the Instrument Cluster. By adjusting the position of the Dimmer thumbwheel on the IP Dimmer Switch, a variable voltage is supplied to the system lamps and components.

Voltage is available at all times at PARK LPS Fuse 9. This voltage is supplied to the Headlamp Switch through the ORN (240) wire. With the Headlamp Switch in either the Park Lamps or the Headlamps position, voltage is available to the rheostat of the IP Dimmer Switch. Depending upon the position of the Dimmer thumbwheel, a variable voltage is supplied through the DK GRN (44) wire to ILLUM Fuse 14. This voltage is then distributed to the system lamps and components by the GRY (8) wire. The illumination lamps in the Instrument Cluster and the Heater and A/C Controller are grounded by the BLK (150) wire at Ground G201. The illumination lamps in the front auxiliary heating and/or air conditioning components, when supplied, are grounded by the BLK (ISO) wire at Ground G400. These lamps respond directly to the voltage supplied to produce variable levels of illumination.

The Radio and the Instrument Cluster's PRNDL and Odometer indications do not operate directly from the incoming voltage on the GRY (8) wire. These components use the variable voltage as a setpoint signal to adjust the component's illumination as powered from another circuit. The Radio's illumination circuit is powered from RADIO I Fuse 17 through the YEL (43) wire. It is grounded by the BLK (150) wire at Ground G201. The Instrument Cluster PRNDL and Odometer illumination circuits are powered from TRANS Fuse 20 through the PNK (1020) wire. The Instrument Cluster's electronic ground is at Ground G101 through the BLK/WHT (451) wire. With no voltage on the GRY (8) wire, the illumination levels for these components are set for daytime brightness. With voltage on the GRY (8) wire, the brightness is set by solid state electronics in proportion to the voltage set by the Dimmer position.

The Instrument Panel Dimming voltage level to the Radio and to the Instrument Cluster's PRNDL and Odometer indications can be overridden and the illumination levels restored to full brilliance even though the Park Lamps or Headlamps are on. This is done by placing the IP Dimmer Switch's thumbwheel adjustment in the Parade Mode detent position. (This is shown as the Parade Mode Switch.) With the switch at the Parade Mode detent, voltage from PARK LPS Fuse 9 is applied on the PPL/WHT (1382) wire. With voltage present on the PPL/WHT (1382) wire at the Radio or the Instrument Cluster, the illumination levels for the Radio, PRNDL indication, and Odometer are at full brightness.