Cluster Illumination

The EMIC has several illumination lamps that are illuminated when the exterior lighting is turned on with the headlamp switch. The illumination intensity of these lamps is adjusted by the panel lamps dimmer rheostat when the headlamp switch thumbwheel is rotated (down to dim, up to brighten). The illumination lamps receive battery current through the panel lamps dimmer rheostat and a fuse in the JB on a fused panel lamps dimmer switch signal circuit. The illumination lamps are grounded at all times.

In addition, an analog/digital (A/D) converter in the EMIC converts the analog panel lamps dimmer rheostat input from the headlamp switch to a digital dimming level signal for controlling the lighting level of the VFD units on the cluster circuit board. The EMIC also sends electronic dimming level messages over the PCI data bus for use by the Compass Mini-Trip Computer (CMTC) and the radio in synchronizing the lighting level of their VFD units with that of the EMIC VFD units. The headlamp switch thumbwheel also has a Parade Mode position to provide a parade mode. The EMIC monitors the request for this mode through a hard wired day brightness sense circuit input from the headlamp switch. In this mode, the EMIC will override the selected panel dimmer switch signal and send a message over the PCI data bus to illuminate all VFD units in the vehicle at full (daytime) intensity for easier visibility when driving in daylight with the exterior lighting turned on. The parade mode has no effect on the incandescent bulb illumination intensity.

The hard wired cluster illumination lamps may be diagnosed using conventional diagnostic methods. However, proper testing of the VFD unit dimming level and the electronic dimming level messages sent by the EMIC over the PCI data bus requires the use of a DRBIII(R) scan tool. Refer to the appropriate diagnostic information.