The wipers almost always working erratic(1/50 working O.K.),after turn on they start work,but when turn off they still works and after some time stop in the incorrect position,not to the lower edge of the windshield but to the random place of the windshield.To turn on again,have to reset on/off.Only way to turn off by yourself is to turn off the ignition switch in the moment when the wipers reach the lowest edge of the windshield and not earlier or later.How to fix?