I know this is old, but I just did this on a 78 W150, but reversed P1 and P2 from the attached diagram. At least in 78, P1 should be always hot and P2 should go to the Park wire on the Cole Hersee switch. Check the continuity of your existing switch, but I think they used the same 2 speed switch for many years. With a standard 2 speed motor that doesn't reverse directions, you have an internal ground pole through the wiper motor frame, either A(low) or H is connected to B when the switch is on, P1 is always connected to B in all positions and continues to drive the motor when the switch is turned off until it returns to the park position and is disconnected. P2 doesn't do anything in the standard switch, but the CH 75600-04 switch uses the pulse for the intermittent function.
