Backup Lamp Switch: Description and Operation

Fig.2 Backup Lamp Switch - Typical:

Vehicles equipped with a manual transmission have a normally open, spring-loaded plunger type back-up lamp switch. The backup lamp switch is located in a threaded hole on the side of the manual transmission housing, beneath the floor panel of the vehicle. The backup lamp switch has a threaded body and a hex formation near the plunger end of the switch, and an integral connector receptacle at the opposite end of the switch. When installed, only the connector receptacle and the hex formation are visible on the outside of the transmission housing. Vehicles with an optional electronic automatic transmission have a Transmission Range Sensor (TRS) that is used to perform several functions, including that of the backup lamp switch. The TRS is described in further detail elsewhere in this service information. The backup lamp switch cannot be adjusted or repaired and, if faulty or damaged, the entire switch unit must be replaced.

The backup lamp switch controls the flow of battery current to the backup lamp bulbs at the back of the vehicle through an output on the back-up lamp feed circuit. The switch plunger is mechanically actuated by the gearshift mechanism within the transmission, which will depress the switch plunger and close the switch contacts whenever the reverse gear has been selected. The switch receives battery current through a fuse in the Junction Block (JB) on a fused ignition switch output (run) circuit whenever the ignition switch is in the ON position. A take out of the engine wire harness connects the backup lamp switch to the vehicle electrical system. The backup lamp switch and circuits can be tested using conventional diagnostic tools and methods.