The front two leads are the normally open circuit. When the pedal is pressed, it supplies power to the wiper motor. Once the wipers are past a certain point, the wipers get power through the switch actuated by the wipers position. The problem is that that puts a voltage potential on the side of the foot pedal which usually doesn’t have power, and if you splice a pump in to the line, the pump runs whenever the wipers do, and that includes when the regular wiper switch is turned on. The solution is to splice the pump motor in and then insert a diode which only allows current flow one way. E.g. through the foot pump switch to the wipers and the pump, but not from the wiper motor to the pump. The advantage is it can all be done without removing the foot pump or modifying it an any way.