Understanding this part of an automotive wiring schematic
Mechanically operated switch

So that the wiper can always go back to the starting point, even if the relay turns off when it's half way up the screen.  It's drawn a bit funny - normally you'd only draw one of the branches. The wiper can run from the always-on input at any point in it's travel except the home position.  There, it needs power from the other input, the relay-controlled one, to start it off.  

One of the comments suggests this is a reversing switch, but I don't think that's right.  Reversing switches would need to be wired more like a H-bridge, and would be in series with this switch.  Most cars do not use a reversing switch, instead they use a mechanical mechanism to turn a continuous rotation of the motor into reciprocating motion of the wiper.

[Image from http://ch00ftech.com, where someone is trying to make their wipers move in time with the beats from the stereo]

The green pin (P1) goes to the motor, and is always connected to the metal track on the green disk.  P2 is connected to the always-on power, so most of the time the metal track connects the motor to the power.  When the wiper is in or near the home position, the P2 pin is not touching the metal track, so the motor is not powered.  The switched live (A in your schematic) is separately &amp; permanently connected to the motor.  Most cars use something similar.