How I converted my Farmall 100 to 12v 

I used a 10SI Delcotron to replace the old 6v Delco generator on my Farmall 100 and converted the tractor to 12v. I wired the Delcotron up basically as shown in most early 1970's GM service manuals which was fairly simple and straight forward as described in the video:
10AWG from bat terminal on Delcotron to "load"/generator terminal of ammeter.
14AWG from no. 2 terminal of Delcotron to "load"/generator terminal of ammeter.
18AWG from no. 1 terminal of Delcotron to switched side of ignition switch with an indicator light bulb in series with the switch and terminal. Bulb is 14v 3.8W.
Remember, when using a 10SI Delcotron, wherever you connect the no. 2 wire is going to be the point in the system that the Delcotron's internal regulator will use to control the voltage output.
When you convert from positive ground to negative ground, you do not need to reverse the bat/generator leads on the ammeter. The ammeter does not care about system polarity.