WARNING: This page is about a different car, the 2010 Porsche Cayenne, 2009 Porsche Cayenne, and 2008 Porsche Cayenne. However, it is still accessible from the selected car via links, so may be relevant.
-A-
Insert the light switch plug until it clicks into place.
Fig 1: Inserting Light Switch Plug
Courtesy of PORSCHE CARS NORTH AMERICA, INC.
-B-
Insert the light switch to its limit and turn the rotary knob anti-clockwise.