Older tractors have externally regulated generators or externally regulated alternators, in some instances. That means there is one device that turns energy from the fan belt into electrical energy, Generator Regulator and another device, called a regulator, that keeps the voltage from overcharging the battery. This is a very simple description but it will work for our needs.
Modern alternators offer improvement to an older tractor's charging system and cost far less.
This article addresses the electrical adaptation of a modern alternator to an older tractor. I used a Datsun alternator for my Massey Ferguson because the diameter was the same as the original generator. Before you begin you need to make sure your system is a 12v, negative ground charging system. If your system is something else, you must make this conversion before continuing with an alternator upgrade. You may wish to save these parts for a future classic restoration.