Principles of Operation
WARNING: This page is about a different car, the 2007 Lincoln MKX and 2007 Ford Edge. However, it is still accessible from the selected car via links, so may be relevant.
The transaxle is hardwired to the PCM which monitors the transmission gear status. When the PCM detects the transaxle is in REVERSE (R), the PCM provides ground for the reversing lamps relay coil. When the reversing lamps relay is energized, voltage is routed to the reversing lamps.