Old Delcotron. I used one for years. A little big, a little heavy, but it works. Kept the batteries up. Doesn't cost hundreds of dollars, And what I like about it, the thing is easy to work on in the field. I carried parts for it and had to fix it at the track one or twice.

Self exciting regulator makes it a one wire. Most companies plug the hole so the two wire plug can't be used.