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Test voltage at the battery with a multimeter. Analog works best around spark-ignition engines because digital may freak out from the RF noise from the ignition system. The charging, voltage at the battery should be between 13.8 and 14.5 Volts. If the battery has a reasonable amount of charge, but the charging system is not working, the battery voltage will be 12.5 Volts, or less. If you read less than 13.5 volts at the battery, check from the "A" (armature) terminal on the generator to chassis ground. If the voltage here is less than 13.5 Volts, connect a jumper wire from the "F" (field) terminal on the generator to chassis ground. (Make sure connections are clean.) This is known as full-fielding the generator, and should cause it to put out MAXIMUM Voltage. If it charges big time with the field grounded, suspect a broken wire, a broken ground strap or bad connection at the regulator, or a bad regulator. If there is no output from the generator with the field terminal grounded, try POLARIZING the generator. ENGINE OFF. Momentarily connect a heavy-gauge jumper between the "BATT" and "A" terminals at the voltage regulator. (Sometimes the "A" terminal is labeled "GEN"). Start engine. If still no generator output with the "F" terminal grounded, you have a bad generator. Disassemble generator and check for worn or stuck brushes. Blow out dust and dirt with compressed air. Take a broken hacksaw blade, and grind it a little thinner in the tooth area, and carefully clean the slots between the copper bars on the commutator. Wrap a strip of sandpaper around the commutator, and lightly sand the commutator while turning the armature to get an even job all the way around. Blow the armature and commutator clean with compressed air. A check with an ohmeter should show continuity between all commutator bars, and NO continutity from any of the commutator bars to the metal shaft of the armature. Check for shorts from the "A" and "F" terminals to the metal housing of the generator. There should be continuity from the "A" terminal to the "F" terminal through the field windings. With an accurate ohmmeter, you should get a resistance through the fields of somewhere in the 5 - 15 ohms range. (I'm guessing at that reading, as I'm away from my reference books at the moment). If brushes are good and able to move freely, and no obvious shorts are found, assemble the generator and reinstall it. Polarize it again and start tractor. If it still does not work, there may be other problems inside the generator that will take more test equipment (a GROWLER) to find, so a trip to a repair shop will be in order!
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