I have a John Deere LX279 mower with a kawasaki 17 horse v twin OHV liquid cooled engine. It will not shut off with the key. I have been shutting it off by unhooking the negitive cable from the battery. Is this a computer board problem or some thing else. It is not a magnito ignition because it has a coil ignition on it. I can work on just about anything but just need to know where to start. Any advice would be appreciated Thank you