[FRED]

Next time it does this pull the plug off the wiper motor while the wipers are running (wiper switch in off) then put the wiper motor plug back on. Do the wipers start running again with the key OFF or not. Looking for a clue. Most likely it's one of the wiper relays inside the switch itself.

Or try this. Key to ON wiper switch OFF. If the wipers are not moving, well that's good. But now get a piece of elect wire bare at each end. PUt one end in the back of the Blue/Red wire at the wiper motor and the other end of your new wire to a nearby ground like the engine itself. Wipers should start wiping. Now unground your wire and see if they stop running or not. What happened? The Blue/Red and Blue/White wires are the wires that you put a ground on with the switch when you turn the wipers on. So you can also try this with the blue/white wire. Key must be ON and be sure your wiper switch is off when doing this.

No harm whats so ever will happen doing this IF your not color blind.