[cdmulders]

If this picture is from a euro-spec E89, then it is likely a rear fog light. Most euro-spec cars have rear fog lights. Several countries make them mandatory. They are often built right into the existing tail light clusters. I retrofitted my F10 to have rear fog lights by simply replacing the switch on the dash to include a button that looks just like the one on your picture, and the car was already wired so that the rear fog lights worked right away on my Canadian-spec F10 after I replaced the switch module. From my experience in Belgium with my Canadian-spec E89, I do not believe just replacing the switch on the dash will activate a north-americas spec E89, as the tail lights are actually mildly different in Europe. There was a thread on this topic on this E89 board a few years ago.