I've got another 500 King Quad with a burnt out 4WD shift motor in at the moment. It seems to be a fairly regular failing and would be no big thing if it wasn't for the extortionate price of a new "unit" which seems to be circa $630 or £520 in the UK. The problem, when you open the unit up, is a kids toy car type electric motor, which burns out. Similar motors are on eBay for $5 but I once tried one and it was wrong polarity, and not powerful enough when I did manage to change polarity. So, please someone, find the right motor and sell them to us for a reasonable price. Also noted on this one, the heads on the mounting bolts were corroded away, just enough hexagon left to loosen them, on a 4 year old bike. I suspect removal on older machines would be a "remove diff and drill the heads off" job.