I had a similar problem with an s1300 at work. Tracked it down to a broken spade end clip. It was located under the left side of the foot rest. A wire goes to the motor above the cutter deck. There is a pair of clips & it wasn't obvious until I took them off that 1 was broken as they have plastic covers. Only took a few minutes to fix with a new clip. Hope that is of help.
Steve, July 2009