Principles of Operation
WARNING: This page is about a different car, the 2009 Mercury Milan, 2009 Lincoln MKZ, and 2009 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
The smart junction box (SJB) is also known as the generic electronic module (GEM).
The SJB monitors the headlamp switch position by sending a voltage reference signal to the headlamp switch. When the fog lamp switch is engaged, the voltage reference signal is routed to ground.
The fog lamps can be turned on when the following pre-conditions are met:
- The ignition switch is in the RUN or START position
- The parking lamps are on
- The high beams are off
When the SJB receives an input from the headlamp switch indicating a request for the fog lamps (and the pre-conditions are met), the SJB provides voltage to the fog lamp relay. When the fog lamp relay is energized, voltage is routed to the fog lamps.