That circuit breaker is opening because you have something pulling too much current. When that happened on my tractor, it was the fuel cutoff solenoid. The solenoid is at the rear of the injector pump and has a single wire going to it with a spade connector. Disconnect the solenoid and then reset the breaker. Turn the key on and see if it opens again by itself. Your tractor won't start if your solenoid is unplugged, but if the CB stays set, then plug the solenoid back in and see if it trips. If it does, then the solenoid is pulling too much current. My solenoid got very warm on my tractor and when I tested it on the bench, it burned up since I didn't have any fuse or CB in line. I don't know if that's your problem, but it might be.
Another problem might be a faulty glowplug timer and/or glowplug relay. If you can identify exactly what fuse/CB number is opening, then you can investigate each thing on that circuit individually. I don't have the circuit diagrams for your tractor, but surely somebody who does will see your post if you tell us exactly which fuse/CB position is opening. My owner's manual shows a chart/table of fuses and what they power. Surely your owner's manual has the same thing for your tractor.
