If you have decent jumper cables, use them to jump from your vehicle to tractor and see what starter does on 12v. So as to leave tractor cables, connections, switch "as is" as much as possible, remove the cables at the battery and connect jumpers to those cable ends. Leave ignition OFF, so as to avoid placing 12 volts on anything other than starter. 6v battery is totally out of picture. If you wish to be extra cautious, you can remove wire from BATT terminal of cut out, but since a good cut out will be open, it shouldn't matter.
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