When you place the gear selector lever in REVERSE, the remote function actuator (RFA) module receives a message from the powertrain control module (PCM) through the class 2 serial data line. The RFA then grounds the PERIM LP relay coil. The relay switch then closes, supplying battery positive voltage (B+) to the backup lamps. The backup lamps ground permanently at G400. The RFA removes the ground to the PERIM LP relay when the PCM sends the class 2 serial data line message to the PCM that the gear selector is not in REVERSE. The PERIM LP relay switch then opens, removing battery voltage from the backup lamps and they then turn off.