Tractor Repair: 12 volt conversion, auto parts supplier, allis chalmers

Question
I have a 1955 Allis Chalmers B that I want to convert to 12 volt. I printed your instructions for changing a Fergeson from 6v to 12v. Is this the same? Allis is 6v positive ground, has off/on switch and amp gauge-no lights. What value diode do I use on alternator field wire (part # etc.). Is a GM Delcotron a good choice for the alternator?

Answer
  Hello,

  Yes, the procedure is pretty much the same for converting any 6 volt positive ground tractor.  Not sure what you mean by what value diode, you might be thinking of a resistor instead.  If you use the
Delcotron with internal regulator, it is very easy to hook up, but you need the diode to only allow current to flow into the alternator on the field wire, and not back out.  Because the alternator field terminal and the coil + terminal are both connected to the ignition switch, current feeding back from the alternator will supply power to the coil and make the engine stay running when you try to shut it off, unless you put the diode in to act as an electrical one way check valve.  There is a flat plastic connector available that plugs into the terminals of the alternator, and it has wires and the diode already there to splice onto the tractor wires.  I don't know the part number of this connector, but we get them from an auto parts supplier.  An experienced auto parts person should be able to help you get one.  The other option is the type of alternator that only has one wire and does not need a field wire and diode, but they're very expensive.  I can get a reman 60 amp Delcotron for about $70 versus $200 for the one wire type.

                  Good luck,

                       Arnie