3-speed-wiper questions

After decoding the fender tag I noticed that my 74 Dart should have a 3-speed-wiper...

In fact it seems that I've only a 2-speed. Out, slow, fast.

For what is the 3rd speed? Interval?

Another problem: if I switch off, the wiper-blades stop immediately, so that I've to wait untill they are at the bottom of the screen.

Is this causing in a defect motor? Or is there somewhere a relais?

Help needed... :-(