I shot the following video while I was trying to figure out how to disable the PTO Safety switch on my Craftsman LT1000. There are 4 wires going into the switch. Two are black, and two are yellow. When the PTO is disengaged, the two yellow wires have continuity through them. The black wires do not. When you engage the PTO, the black wires have continuity through them and the yellow do not. If you tie the yellow wires together and tape the black ones up so that they cannot make contact, you will have defeated the safety switch.
Eventually, I'll probably do a fearless front rewire of the tractor. But this is better than having to hold the button in when I want to start the tractor.