A couple of days ago there was a posting in regard to a similar problem reported. I believe this complaint was for a 240, but the same or similar cause may apply.

This posting was related to the fact that when the headlights are on (high maybe) the wipers come on. The proposed problem is that there is a bad ground for the headlights. The current then flows through the next least resistance path. This path for the headlights is apparently through the wiper motor. Check the headlight wiring and make sure the grounds are secure before replacing the switch. For reference the switch is about $10.00 at the local self serve auto recycling center in my area.

Hope this helps.

Dan