Help me understand what you mean by "jumper the ignition switch" and crank the engine -- do you mean that you jump terminals "B" to "S1" on the key switch as shown in the diagram above? OR, do you mean that you jumped the solenoid?
If you can crank the engine but it still does not fire -- very likely the safety switches are not in their correct states (seat switch not working as it should, PTO switches not in the OFF position, or some wiring error...etc.)
Did this just start to happen and the tractor used to start and run as it should, or is this a tractor you have never had running? Tell us more about what you know...