How to Convert a Tractor to 12 Volt


Converting the electrical system of an antique tractor to 12 volts from the original six volts is a good idea for several reasons. Brighter lights, faster starting and cheaper electrical components head the list. An ideal time to do so is when the original six-volt generator has problems, because replacing the generator with a 12-volt automotive alternator costs less than rebuilding the generator. You can reuse the original wiring if it is in good condition, since the new 12-volt components will use less current than their six-volt counterparts. You will also be converting from the original positive-ground system to a more modern negative-ground system.

Things You'll Need

  • Delco internally regulated automotive alternator
  • Steel bar stock, 1/8-inch by 1-inch
  • Hacksaw
  • Drill and bit set
  • Wrench set
  • Volt-ohmmeter
  • 16-gauge insulated wire
  • Crimper and terminal set
  • Ignition ballast resistor
  • 12-volt light bulbs
  • 12-volt battery
  • Remove the old generator and replace it with the 12-volt alternator. If the mounting holes on the alternator don't match the existing bracket, cut and drill a piece of the bar stock to adapt. Remove the original voltage regulator, as you will not be reusing it.

  • Connect the large-gauge wire from the battery to the "Bat." terminal on the alternator.

  • Connect a short 16-gauge jumper wire from the "Bat." terminal to the "2" terminal on the alternator.

  • Locate a connection that is energized when the ignition switch is on. This will be one of the wires that connected to the original voltage regulator. Connect a 16-gauge jumper from this connection to the "1" terminal on the alternator.

  • Replace all light bulbs with their 12-volt equivalent. Tractor parts stores and auto parts stores can cross-reference these for you.

  • Disconnect the wire from the "Bat." terminal of the ignition coil. Connect the ballast resistor between the wire and the coil.

  • Replace the six-volt battery with the new 12-volt battery. Connect the ground cable to the negative post and the nonground cable to the positive post of the battery.

Tips & Warnings

  • Double-check your work before connecting the battery.
  • Do not crank the starter for more than 10 seconds, as it will become hot more quickly than it did with six volts.


  • Photo Credit Vintage Orange Tractor image by Joy Prescott from
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