welcome to the site!
1. That vacuum diaphragm controls a 2-speed gear box for your speedo so that when you shift the 2 speed rear into low, your speedo shifts into low as well and still shows the correct speed. necessary? no, always accurate? no. available, no! lol. in my experience, I use low on the rear when towing and pulling up a hill, with my foot in it, that means low or no vacuum which means, the speedo stays in high anyway. It is cool to have it working though!,
2. there are only 2 wires going from the motor to the switch, but it is a 2 speed. The switch supplies ground, + is supplied by a wire from the key switch (that is why the wipers stop as soon as you turn off the key, and do not return to park. The park function has a separate ground, which may be a bit dirty and the reason the park function is real slow. Mine is as well, most of the time!
