When the ignition switch is in the RUN position, voltage is available at the backup lamp switch from circuit breaker 9 through CKT 139 (PNK). The backup lamp switch is located on the transmission. When the transmission is placed into reverse, the backup lamp switch contacts close. This applies voltage through CKT 24 (LT GRN) to both backup lamp assemblies. Voltage is also available to the backup alarm, if equipped. The backup lamps ground is provided through CKT 150 (BLK) to ground G405. When voltage is applied while the transmission is in reverse, the lamps illuminate. Shifting to another gear or turning the ignition switch OFF causes the lamps to turn off.