I am not familiar with your wiper switch problem. But I had the same experience with my turn signal switch. Just the slightest disturbance would knock the switch into the high beam mode. That is actuallly a very common problem. I was able to reair the switch on my '79SC. Here are a few links describing the procedure:
Headlight hi/low beam issue - newbie
Hi Beam Switch: Poof! Headlight Switch OK?
Lost my low beams.
turn signal switch quick fix pictures
Problem with Steering Column Switch
Hope it helps. While you are at it you should make sure to have the after market relays installed. Those will keep the hight lamp current away from the signal switch and possibly fry it. The relay kit is available from our host.