The very best fix would be to diagnose the problem and have put it back to the way it worked from the factory. I don't know why you want to tie the fan directly to a switch but having things work "as designed" is the best option. I would troubleshoot and go back to factory setup or you could be asking for problems not only now but especially if you decide to sell it. The two best ways to drop the selling price on your atv by half is rig some wiring or add a snorkel, serious red flags.
2007 Foreman 500FM
2014 Foreman 500FM