you start with the tractor's battery. Clean it's connections as O)liver detailed. Try starting. If still just a click, take apart and CLEAN all the other heavy wire start circuit connects. Pay close attention to connection surfaces being clean, bright.I've tried even hooking it up to a jumper box because I wondered that is it possible it solenoid is bad?
Don't use your best shiny new screwdriver since it might make a couple small burn marks.
You can eliminate the solenoid very quickly. Take a good-sized screwdriver and jumper across the the 2 large terminals on the solenoid (the ones with the red covers). If it cranks the engine the solenoid is bad. If it doesn't, you have problems elsewhere - battery, cables etc. Don't use your best shiny new screwdriver since it might make a couple small burn marks.
Bob B.