Interior Lamps Dimming

The dimming of all instrument panel incandescent lamps and vacuum fluorescent displays is based on the value of the driver-adjustable dimming control on the Headlamp Switch. The dimming of the vacuum fluorescent displays and the incandescent backlighting is only possible when the park lamps are on.

Incandescent Dimming
Whenever the park lamps are on, voltage from Fuse D13 is applied to the Headlamp Switch at connector C2 terminal B. This signals the Headlamp Switch's PWM module to generate a pulse width modulated signal based on the position of the dimmer control. The Headlamp Switch (at terminal C2/C) applies the pulse width modulated signal to the incandescent lamps and the Instrument Panel Cluster's dimming input terminal C1/C10. The bulbs with this signal applied will dim or brighten depending on the frequency of the signal generated.

Vacuum Fluorescent Dimming
Whenever the park lamps are off no voltage is applied to the park lamps on input terminals on the Instrument Panel Cluster (terminal C1/D3) and Radio Control Head (terminal C1/7 or 6). This signals the cluster and radio vacuum fluorescent displays to be at full brightness.

When the park lamps are on, voltage from Fuse D13 and/or D11 (CKT 9) is applied to the cluster's and radio's park lamps on input terminals signaling them to respond to the dimming control in the Headlamp Switch.

Dimming of the vacuum fluorescent displays are controlled by the Instrument Panel Cluster based on the pulse width modulated signal applied by the Headlamp Switch to the cluster's dimming input terminal C1/C10. In response to the dimming input signal the IPC generates a pulse width modulated signal at terminal C1/C6 (CKT 724) to dim the Radio/Radio Control Head. As the on time (duty cycle) of this signal increases the vacuum fluorescent display of the Radio/Radio Control Head gets dimmer. In addition to controlling the Radio/Radio Control Heads dimming, the cluster also supplies 16 volts at terminal C2/B2 through CKT 726 to power the Radio/Radio Control Head's vacuum fluorescent displays. The cluster supplies this voltage whenever the ignition is in RUN.

Export Harness On Vehicles Equipped With Export Harness
The Instrument Panel Dimming system operation on export vehicles is the same except a Panel Lamps Inhibit Relay Circuit is added. The purpose of the Panel Lamps Inhibit Relay is to prevent the panel dimming operation when the daytime running lamps mode is activated. Export vehicles without Daytime Running Lamps do not use the function of the Panel Lamps Inhibit Circuit. The park lamps on signal (CKT 9) will always pass through the normally closed contacts of the Panel Lamps Inhibit Relay. The jumper wire at CKT 592 connector C113 is not connected and the relay will not energize.

Export Harness With Daytime Running Lamps (T61)
The Panel Lamps Inhibit Relay's switch contacts are in series with the park lamps on input terminals on the Headlamp Switch (C2/B), Instrument Panel Cluster (C1/D3) and the Radio Control Head (C1/7). These terminals turn on the dimming circuits when voltage is applied to them.

When the park lamps are on voltage would normally be applied to the park lamps on input terminals but when the daytime running lamps mode is active, the Panel Lamps Inhibit relay energizes, interrupting the circuit path to the park lamps on input terminals.

Voltage from Fuse C5 is applied to the Panel Lamps Inhibit Relay coil at all times. The relay energizes when the Twilight Sentinel/DRL module grounds the relay at its DRL control terminal (4B). This occurs whenever the Twilight Sentinel/DRL Module is in the daytime running lamps mode.