explanation on how 2 speed wiper works

My 71 scamp originally had a foot pump washer with a 2 speed wiper. No extra connector for the washer output.

Wow...I woulda thought they were done with the foot pump by 71.
Stupid question, but is your switch 2864415? If so, try just pushing the switch in to see if it has a "wash" function? I would think that the switch would be the same for both, just that if it gets a foot pump then they "omit" the connection to that part of the switch??