Principles of Operation
WARNING: This page is about a different car, the 2011 Mercury Milan, 2011 Lincoln MKZ, and 2011 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.
For vehicles equipped with an automatic transaxle, the PCM (2.5L or 3.0L engine) or the Transmission Control Module (TCM) (3.5L engine) controls the coil ground side of the reversing lamps relay. When the vehicle is in reverse, the PCM or TCM energizes the reversing lamps relay to provide voltage to the reversing lamps.
For vehicles equipped with a manual transaxle, the reversing lamp switch controls the coil ground side of the reversing lamps relay. When the vehicle is in reverse, the reversing lamp switch contacts close to ground, energizing the reversing lamps relay to provide voltage to the reversing lamps.