Principles of Operation
WARNING: This page is about a different car, the 2007 Mercury Mariner and 2007 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.
The smart junction box (SJB) monitors the multifunction switch position by sending a voltage reference signal to the multifunction switch. When the multifunction switch is in the AUTOLAMPS ON position, the input signal is routed to ground.
The SJB also monitors the light sensor with a voltage reference signal. The light sensor input to the SJB varies with the ambient light conditions.
When the SJB receives an input from the multifunction switch indicating a request for the autolamps, the SJB then monitors the light sensor for the ambient light condition. If the SJB determines the ambient light level is dark, the SJB supplies voltage to the exterior lamps.