My ambulance has more power drain than any tractor that I can conceive of having. There is no one wire other than the supply to the starter that is greater than a 10 or 12 gauge wire. The fuse blocks are supplied with power from a master battery disconnect terminal and then the power goes to the individual circuits that are protected by individual circuit breakers. As an example, if I were to make a hot run with all lights and siren going for 20 minutes, that would be enough to kill both batteries. The alternator puts out 220 amps and the batteries are both extremely large. This is why you don't ever see them shutting down the fire truck, ambulance, or police cars, because if they do, they might not get them started again. This drain will suck a system dry, but never overload the wiring of the system.
If you were to add up the total amount of amperage that each circuit breaker in your home electrical panel and compare that to the total amperage service that supplies that panel, you will see the disparity. 200 amps might be what supplies the panel, but the total breaker capacity might be 1000 amps or more. You will never draw that much all at once, so there is never a problem. Same with your tractor, it is doubtful that you will ever draw the full capacity. Remember, the fuse or circuit breaker is designed to protect the wiring from over current, not the device.