Well thanks for all of the suggestions if nothing else I have learned that its not OEM and had few laughs. I will just have to trace the wires this weekend and see where they go. I will post back in this thread and let you guys know what the hell this button controls.
Would be funny if it did kill the rear plate lamps.
2007 335i sport sedan fully loaded, fmc, downpipes, FTP custom tune.
2012 X5 50i fully loaded.