Originally Posted by AMGLover

Second pull will turn the rear driver side stop light on "fog mode" This is an inherited Mercedes feature, the rational being you are driving in fog and people behind you may run up on you at autobahn speeds... so the Germans standardized on the driver side to be the bright warning light - you will also see this on Audi's and BMW's. I actually never have checked to see if the feature "works" on the Xf...

- ej