How to Test a Farmall Tractor 6 Volt Generator

A 6-volt generator serves the same purpose as a 12-volt alternator — it charges the battery. If the battery does not take a charge while on the Farmall tractor, but you do not think the battery is bad, a logical conclusion is that your generator is bad. However, before you remove the generator to replace it, make certain that the generator is the problem. There are two means of testing the generator and even if it is not working, it may not be defective. It may simply need to be polarized.

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A volt meter will tell you if your generator is working or if you can move to the next step of your troubleshooting.

Step 1

Turn off your Farmall. Place the positive probe of the voltmeter on the positive terminal of the 6-volt battery and touch the negative probe to the frame of your tractor. If the battery is charged, the voltmeter should indicate 12.6 volts, within a few 10ths of a volt.

Step 2

Fire up your Farmall and touch the positive probe to the positive terminal and the negative probe to the negative terminal — or the frame of the tractor — while the engine is running. If the generator is charging, the voltmeter will indicate the voltage is within a few 10ths of 14. If the number remains close to 12.6, the brushes of the generator are probably worn.

Step 3

Test the brushes by putting on your rubber gloves and pushing the brushes of the generator up against the generator casing with the stir stick. Observe the voltmeter. If the numbers change, the problem is the brushes of the generator. However, if the numbers do not change, the brushes may not be the problem. Test your generator the second way.

Step 4

Unscrew the nut on the regulator side of the generator with a wrench and remove the wire from the generator terminal. Clip the jumper wire to the frame of the Farmall and to the DF terminal of the generator. Start the tractor and raise the rpm to 3,500. Touch the positive probe of the voltmeter to the D+ terminal of the generator. If your voltmeter reads within a few 10ths of 35, the generator is good. If the generator is good, but it is not charging, it may not be polarized.

Step 5

Turn off the tractor and remove the fan belt with your wrench set. Start the Farmall. Wait until the generator shaft begins to spin. Connect the second jumper wire to the D+ terminal of the generator and touch the frame of the tractor for three seconds. This should polarize your generator. If the generator shaft does not begin spinning within a few seconds, the generator is likely defective.