GM Service Manual Online
For 1990-2009 cars only

Power is supplied to the headlamp switch and park lamp relay at all times through CKT 240 (ORN). When the headlamp switch is placed in the HEAD or PARK position, current flows to the dimmer control portion of the headlamp switch. When the headlamp switch is in the AUTO position, current flows to the dimmer control portion of the headlamp switch via CKT 74 (LT BLU) from the park lamp relay when the relay is energized by the body control module (BCM). The dimmer control regulates the amount of voltage sent through CKT 44 (DK GRN) to the ILLUM fuse 12 in the IP fuse block in order to control the intensity of the interior lights. From the ILLUM fuse 12, current flows through CKT 1220 (GRY) to the illuminate the following components:

    • The HVAC control panel
    • The fog lamp switch
    • The supplemental inflatable restraint module switch
    • The transfer case switch
    • The radio
    • The IP cluster

CKT 1220 also supplies a dimming input to the BCM . The lamps are grounded through CKT 1050 (BLK) to G203.