Principles of Operation

WARNING: This page is about a different car, the 2013 Ford Mustang. 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 signal to the headlamp switch. When the fog lamp switch (part of the headlamp switch) is engaged, the voltage reference signal is routed to ground.

The fog lamps can be turned on when the following conditions are met:

The ignition switch is in the RUN or START position
The low beam headlamps or 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, the SJB energizes the fog lamp relay (integrated into the SJB). When the fog lamp relay is energized, voltage is routed to the fog lamps and the fog lamps on indicator (located within the headlamp switch). The GT fog lamps are equipped with an LED that is only serviced with the fog lamp assembly.