Sounds like you might have a wiring issue or perhaps a safety switch is going out and that is what is causing you issues. Can you trace the wiring harness and look for loose, frayed or pinched wires? Wiring issues tend to cascade and by that I mean one issues leads to an other and so on down the line. Remove, clean and tighten all the grounds first as bad grounds are the cause of many issues. Good luck and let us know what you find.
Tom
Most of the safety switches and wires on the tractor transit through the PTO switch and frankly, once they start aging out, it's a never-ending battle.
Like you, I replaced the PTO switch with an expensive new factory part, but then the seat switch, the reversing switch, the brake switch all gave trouble in turn. The machine just became too unreliable to use. The answer was a complete dewiring of all the switches and then rewiring using new industrial start and PTO switches. Look on line for a wiring diagram which shows just the "Start/Run" and "PTO" circuits in red.
What was necessary on mine is in no means a recommendation for you to remove the "safety" switches, just a statement of what I had to do to keep my two machines operational.
