GM Service Manual Online
For 1990-2009 cars only

Voltage to the radio is available at all times through CKT 340 (ORN). CKT 340 (ORN) provides voltage for radio station memory storage and for the clock memory. With the ignition switch in ACC, RUN, or RAP voltage is supplied to the radio through the RDO 1 fuse (1301). Each speaker has a separate pair of leads. The radio/clock display brightness is at full intensity with the ignition switch in ACC or RUN. The voltage is supplied by CKT 1301 (DK GRN). When the parklamps or headlamps are turned ON, the radio senses the signal and switches voltage for the display from CKT 1301 (DK GRN) to CKT 8 (GRY). Full VFD is achieved by turning the first detent on the headlamp and the parklamp dimmer switch ON. Voltage is supplied to the radio through CKT 1382 (PPL/WHT). The display brightness is then controlled by the headlamp and panel dimmer switch. The radio illumination bulb voltage is supplied by CKT 8 (GRY).