Mine was the relay, it would also stop wherever you turned the wipers off. I never fixed it so can't tell you exactly how.
i had the same problem with my astra, until i was driving home down unlit back roads in the pouring rain and the wipers stopped working all together!
thankfully i had my gf's swimming goggles in the car (she'd been to the gym that afternoon)
so i put those on, wound the window down and 'ace-ventura'd it home! i looked a right state when i got home though lol