There is a lead running from my Sony XNV-L66BT labeled "Illumination", the stated purpose of which is to connect to some other place in the car so that it can know when my headlights are on so that it can dim the display, use night colors for the maps, etc. Does anyone know where this lead attaches? I have a Focus Ghia/Estate from 2007. No clue where to begin with this one.