It might be something in the wiring. Mine would do the same thing from time to time, and it would correspond with a gremlin that pops up from time to time with my dimmer switch, of all things. It's the weirdest thing, I would turn the wiper switch, and while turning the wipers on, the dome light would come on and would dim like a 3 way light switch as I rotated the wiper switch
. It's happened 2 or 3 times in the past several years, and when I turned the wiper switch off, the blades would stop wherever they were instead of parking. It's sporadic, but a similar problem.