I Dont know a whole lot about these cars yet. Sounds like a short somewhere? If it were me, before I'd take it somewhere that will probably charge a lot, I'd start with the trunk area and see if you can check out the wiring right there behind the light and or in the trunk area as best as you can.
Like my 06 300 I had, I finally had a day to take out the whole center console, which wasnt hard at all, and a learning experience. Which also showed me a lot about some other stuff.. But with a newer car like that, or like my 2013 300C, I would probably be more hesitant to actually take it apart haha.. dont want to mess something up.
Or as im sure someone else may already know, could there possibly be a way to reset the Infotainment system? maybe that might work?