Principles of Operation

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 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 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).

On vehicles equipped with the automatic high beam feature, a fog lamps deactivation relay is inline between the SJB and the fog lamps/fog lamps on indicator. This allows the automatic high beam feature to turn the fog lamps off when the high beams are on.