for the rear fog lamp, the reverse lamp gets a red lens. check out the pic of my car. i bought the german-spec taillight assembly when i bought my XF because i've always liked rear fog lamps.



do a search for 'rear fog lamp' or 'headlight switch' -- this topic comes up about once a month.

you are partially right about some MBs (the C and the ML come to mind)... they're using the left-side tail lamp as the rear fog lamp housing. but it is NOT the brake lamp. by regulation, the brake lamp has to be a certain distance from the rear fog lamp. check your g/f's car. when she hits the brake, you'll notice there is a distinct brake lamp bulb and rear fog lamp bulb.