The black box on the wiper motor. 2 options: buy a good used one, or try to repair the one you have. It could be a bad solder joint. Try reflowing the board.

 

Before I bought a good used one from Fred Kiehl, I would play with the different settings, such as wiper delay. I'd allow a complete delay cycle to go through it's delay/wipe and as it was returning to the park mode I would simultaneously turn the switch completely off. In, probably, 7 or 8 times out of 10 times this would work. I also found that not using the wipers first thing after start-up also affected how the wiper motor would function. Play with it and after a while you'll find a way to prolong replacing the motor, or black box, as Fred said to do.