The absolute best thing you can do is to buy the JD technical manual .
It is written inplain language, exlains exactly how to do the test, where to do the tests and what the results mean .
It costs 1 to 2 hours of shop labour so pays for itself the firt time you use it
You have a problem with the seat switch or the PTO switch or the reverse switch or the wiring between any one pair f them