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How to Check the Charging System on 6 Volt POS Ground Farmall Cub

The original Farmall Cub was built from 1947 through 1964 with a 6-volt, positive-ground charging system. Time has taken its toll on the electrical system of these old tractors, and it is not uncommon for a new owner to find that while the starter turns over and the engine starts, the charging indicator needle on the ammeter never moves. Although it is possible to use the tractor for years by connecting a battery charger before each use, it is better to know for certain that the generator is charging the battery.

Things You'll Need

Digital multimeter

Instructions

- 1
  Plug in the test leads and turn on the multimeter. Set the scale for DC volts.
- 2
  Hold the red probe to the positive terminal of the tractor's battery, and the black lead to the negative terminal. The display should read between 6.0 and 6.5 volts. If it doesn't, the battery is at fault.
- 3
  Put the transmission in neutral and start the engine. Allow it to reach operating temperature.
- 4
  Use the multimeter to check the battery voltage with the engine running at half throttle. The battery should read between 7.8 and 8.1 volts. If it does, the charging system is operating correctly.

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