The first question is, is the issue related to the safety circuit or internal to the starter?
It is possible to apply 12 volts to the starter solenoid terminal, to see if the starter works normally. This must be done carefully. There is risk the tractor could move expectantly.
I think this is what I would try first, to eliminate a starter issue from other possible issues.
In the case of my BX2200, believe it or not, the circuit that activates the starter solenoid is completed through the fuel cutoff solenoid. So a defective coil on the fuel cutoff solenoid could also cause the same symptom you are experiencing. Just mentioning this to illustrate that you need to consider even remote possibilities. I doubt your B3030 is the same as my BX.
When troubleshooting the "divide and conquer" approach often pays off. I would eliminate the starter question first myself. If the starter turns, this also eliminates the possibility that the fuel cutoff solenoid might be part of the picture.
However, if I were a betting man, I would bet your issue is with a safety interlock switch. But you will not know until you find the problem.
And you will eventually find the problem...
