What is the extra switch (micro-switch) in the socket for?

The uses of the micro-switch include trailer recognition, disabling parking assistance, or switching off fog lights / switching trailer operation. The micro-switch is an enclosed, water-tight mechanical switch with normally closed, normally open or change-over function. The micro-switch is located in the 7-pin or 13-pin trailer socket and is activated mechanically by plugging the trailer plug into the trailer plug socket.