The dome lamp is located within the cab in the front center part of the headliner. The dome lamp receives power through CKT 150 or CKT 1 (ORN) from circuit breaker  #7.

The lamp is operated by completing the ground circuit. The ground circuit is completed by operating the dome lamp switch (part of the dome lamp assembly) in one of two positions. With the switch in the DOOR position, ground is supplied to the dome lamp by the door switch, through CKT 26 or CKT 148 (RED/BLK), the diode module D 202 and CKT 2 or CKT 149 (RED/YEL). With the switch in the ON position, ground is supplied through an internal chassis ground screw connection, which doubles as a fastener for the dome lamp to the cab sheet metal.