This one is wired a little different for the lights then you describe , it all looks stock and matches the wiring diagram that I have for my model number except there is no 4th wire , the new regulator has a terminal marked "L" and from that terminal the wire goes to one side of the amp meter where another wire branches off to the light switch -------- I think what I sure do is screw a lead to the underside terminal before I tighten up the regulator mounting bolts so i can get to it easy later ------ any ideas on the battery group that is suppose to be in there never had one to start with ????
i know how the 72s are wired i got 2 72s (suburban 12 and ss15). match the letters from old regulater to new one then disconnect wire for lights and run it to extra terminal. old regulater should have letters on terminals might have to wire brush them to find out for sure if not i can tell you but have to look at a couple tractors first.