One of the big solenoid cables goes directly to the starter. You can touch either end of this cable. In fact, you only need to use ONE of the two cables in a set of jumper cables if you use the battery in the tractor. One end goes to the positive battery terminal and the other end you touch to either end of the starter cable. Be advised: This is going to SPARK! DO NOT clamp the jumper cable on the starter cable; just touch it to see if the engine starts to turn over. We are bypassing everything at this point, just to test the starter.
Batteries put out a lot of amperage! Don't touch the jumper cable to any metal portion of the frame or engine or that will be a spark show and you could get burned. In fact, if you don't have any experience with jumper cables, it's best to let someone who does do this procedure. Would hate to hear that you got hurt trying this.