See also:

Removing the ball coupling
Observe the manufacturer's installation instructions. Press the protective cap into the ball coupling recess. Make sure that the protective cap is firmly in place. ...

Cleaning the headliner and carpets
Roof lining: use soft brushes or dry shampoo if it is particularly dirty. Carpets: use carpet and textile cleaners that have been approved and recommended by Mercedes-Benz. ...

The windshield wipers are inoperative
The windshield wiper drive is malfunctioning. Select another wiper speed on the combination switch. Have the windshield wipers checked at a qualified specialist workshop. ...