Just wrapped up a 6V positive ground to 12V negative ground conversion on my 1952 Massey-Harris 30. Posting the details because when I started this I had a hard time finding real numbers on the charging side of it, and most of what I learned applies to any old tractor you would want to convert.

The alternator is a GM Delco 10SI 63A pulled from a Chevy Squarebody. It is a single-wire, self-exciting unit, which is what makes this swap worth doing on an old machine - there is no external regulator and almost nothing to wire.

The hard part is mechanical, not electrical. Fabricating the bracket and getting the alternator aligned took the bulk of the project. The alternator ended up needing to sit about 3/4" forward of where the generator was, toward the crank pulley, to get the belt running true.

On charging speed, which is where I would have wanted someone else's numbers:

- Stock generator pulley at 600 engine RPM gave me just over 13V. Charging, but slowly.
- Stock pulley with the idle raised to about 650 RPM gets me to 14.4V, which is what I was after. I wanted the battery gaining while the tractor idles, not just while it is working.
- A 2" pulley with a 17mm bore on the 10SI should get you 14.4V at 600 RPM without raising the idle at all. I could not source one, so I went the idle-speed route.

I fitted a voltmeter instead of an ammeter. A 60A ammeter is available if you care about keeping the dash period correct, but the voltmeter gives me a much better read on battery and wiring condition. I also replaced the water temperature and oil pressure gauges during the job.

One lesson: I used an external ballast resistor with the coil. There is an internally resisted coil (ABC6158) that would have made the ballast unnecessary. If you are doing this, buy that one. The 55,000V hot coil itself has been excellent - it fires almost immediately on crank.

I wrote the whole thing up with the wiring diagram and the pulley math here:

https://forum.fullsizechevy.com/t/1952-massey-harris-30-6v-to-12v-negative-ground-conversion-delco-10si-wiring-diagram-pulley-math/632

My tractor, my conversion, my writeup. Ask away if anything is unclear.

1952 Massey-Harris 30 6V positive to 12V negative ground