Principles of Operation
WARNING: This page is about a different car, the 2007 Ford Ranger. However, it is still accessible from the selected car via links, so may be relevant.
When the ignition switch is in the RUN position, the smart junction box (SJB) supplies voltage to the digital transmission range (TR) sensor (automatic transmission) or the reversing lamp switch (manual transmission). When the transmission is placed in REVERSE, voltage is routed to the reversing lamps.