A "click" noise when trying to start the tractor may just be a bad battery or a bad ground. Turn on the headlights then have someone watch the headlights while you try to start the tractor. If the headlights dim, you either have a bad battery or a poor ground. If the headlights stay bright, you may have either a bad solenoid or a starter with a "flat spot" or a bad ground. To check the starter for a bad spot or poor ground try to use a jumper directly from the battery to the starter positive connection, with the tractor in neutral. If the tractor cranks you have a bad solenoid. If not, make sure that the starter has a good ground. If there is paint between the starter and the block, the paint can act as an insulator and cause erratic starter function.