1988 310/8 wheel horse tractor?

I put pto in gear an engine stopped.I checked safty switch on pto,there are two.They had alot of play.The only wayI could keep running was to tie switches with pull tie,engine would start.I got new switches was carefull replacing.Engine would not start.When it stopped both times it would turn over but not start.Checked other safty switches seat,clutch,low oil,they all were working.cheched wires into switch,were all on.If i tie new switches together it's starts.Driving me crazy! PLEASE HELP!!!!