could it be?
might also be a bad trans top switch ( check by placing tractor in neutral, blocking clutch down, then using a jumper wire to jump terminal on solenoid hooked to trans switch to ground. )
could also be wire connections.
could be a bad power wire to switched hot connection on solenoid.
could be solenoid itself
or could be the starter.
jump out power and test ground to solenoid.. the easiest to do.. etc..