Why do my windshield wipers short out? on 2008 Buick LaCrosse

When my wipers are set in the intermitent mode they either don't work or run on constantly. When I turn the wipers off they stop in the middle of windshield versus finishing cycle and retreating to the bottom. This only happens when it rains. I test the wipers when it is not raining and they work fine.

Asked by for the 2008 Buick LaCrosse