Unplug it and see what happens.
I will have to take a look myself. curiosity kills.
I think it must have something to do with the brakelights and the license plate light
Ordered 4/26/05. Picked up June 11, 2005. 05 Mustang GT Premium Coupe, 5spd, Performance White, with red accent leather (ICAP), Shaker 500, IUP, active alarm, side airbag, spoiler delete. MODS: Baltimore Street Mods 10' red stripes and red rocker stripe. window tint. K & N aircharger. Pony Package fender emblems. Added 18" Polished Alum. Bullitts Hurst comp shifter