Sooner or later everyone has a similar problem. 50% of time the problem is with one of the safety switches. The options are.
(A) Have dealer come haul tractor to shop.
(B) Use a multimeter to systematically test to isolate problem.
(C) Ask folks on line to take guesses then follow up on each until problem is found or you become frustrated and revert to option (A)
I use option (B). If you have or obtain a wiring schematic it will make it much easier.
Alligator clips on meter leads or assistant to hold meter probs while you activate starter circuit really helps.