Most of the demographic here is afraid of three-wire alternators. The one-wire alternators are self exciting so they need the small pulley for excitation. The three-wire models still need the small pulley because they can't carry a load at low idle, like even the lights. One of the problems with the 10SI alternators is they take cooling air from the front, dust and crap and all, which is ok if you have furnace filter media in front of your radiator to filter the chaff and crap. I used a 85 amp 12SI three-wire that drew air from the rear - as close to a TEFC unit as you can get. McGyver graduated from the Red-Green school. I also used a lap-link V-belt, easy to change if it ever breaks, but after 700+ hours still like new.I put a three wire GM alternator on my Farmpro 2420 years ago. I had to bypass the regulator but it worked perfectly for years. Id guess its still in use on it now. The alternator gauge and light stayed in the circuit. Basically a three wire advantage is it charges even at lower speeds. All it took was a few minor wire changes and I used the belt off a Steiner 420 pto drive (they are a good Kevlar lasting belt) and the holding bracket for a barn door. Good McGyver solutions that stood the test of time for reliable too!