You will need to look at wiring diagram for the machine. I believe it is on
the site here. I would just attach it here but I sure have a hard time
doing things like that. Hopefully one of the technologically advanced folks
here can tell you where it is.
I would start by checking continuity of the wiring involved in the safety
switches. Then begin checking the switches themselves. Especially the
PTO and the seat switches.
Do you have a multi meter you can use to get started?
Ken