There's a contact on a cam inside the wiper motor that takes over from the stalk switch once the motor starts turning. Doesn't affect normal or fast wipes because the stalk switch is always turned on for those, but if that contact is faulty then neither intermittent nor single wipes will work; instead the wipers will stop part way through their travel. For the same reason the blades will not park properly when you switch the wipers off. So, change the motor (or fix the cam contact if you're able).
Keef, March 2010