I posted two schematics in the thread Chris linked. The second one is the one you'll need to troubleshoot your problem. There are four things to check:
1. Seat Safety Switch
2. Operator Safety Module
3. Fuel Shutoff Relay (K5)
4. Fuel Shutoff Solenoid
First, as Chris suggested, try to power the solenoid with a jumper to see that it does work. Then, start looking at the seat switch. If those things don't show as bad, you'll need to take the cowling off under the steering wheel and troubleshoot the relay assembly under the left-side cowling. Your thread title says, "tc45." If you have the gear model, there is a different layout of relays. Let me know which model you have and I'll try to provide you a relay diagram so you can check relay K5 and the Safety Module.