It's quite simple If you want to convert it? Which I have done on a couple of Miller dynamos. You remove the obvious third brush and it's holder (if you want) and the cutout (if fitted) which is often mounted to the side of the dynamo. There should be two wires! one from the field winding 'F' and one from one of the two brushes 'D'. These are wired to the corresponding terminals on the regulator F.A.D.E. A= ammeter E= earth.
Some useful stuff here too. http://www.dynamoregulatorconversions.com/2-brush-dynamo-conversions.php