1950 Farmall Cub with a 12v alternator conversion. It has worked well for years, but now is not charging. Alternator tests "good", and a replacement new alternator also fails to charge. 12v is present from the battery at the main 3-wire alternator lug and one of the other 2 pins, plus the second pin has 12v through a diode that is only on when the ignition is on. Battery is good, but after tractor starts voltage drops about 0.3v and the ammeter indicates about a 1 amp discharge. Fan belt os OK and is turning the alternator. What am I missing here? I had previously noticed the ammeter would "bounce" around a 10a charge in the past, and even saw that briefly during my testing when I first started the tractor, which is why I replaced the alternator since I assumed it must be a bad relay contact or something inside the alternator regulator. Is there another regulator or relay somewhere? This conversion was on the tractor when I bought it 25 years ago, but it looks pretty much like others I've seen.