How to Test a Tractor Generator

by Nathan Fisher
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old tractor image by Edsweb from

The generator was the predecessor to the alternator in both cars and farm equipment. Each supplies electricity to recharge starting batteries and run accessories, but an alternator produces electricity by spinning a magnetic field (magnets) inside a stable bundle of wires, whereas a generator produces electricity by spinning the wire inside the magnetic field. You can test a tractor generator to determine if the armature is working by hotwiring it directly to the battery.

Step 1

Disconnect the negative battery cable with a wrench. Clip the jumper cables to the battery terminals: red to positive, black to negative.

Step 2

Remove the hot (positive) wires from the generator's field and armature terminals with a wrench and screwdriver.

Step 3

Clip the black (ground) jumper cable to the terminal on the generator marked "field." Clip the red (positive) jumper cable to the terminal on the generator marked "armature." If the armature does not spin, it is faulty.

Step 4

Insert the red positive lead from the voltage meter under the red jumper cable clamp.

Step 5

Remove the black jumper cable from the generator's field terminal and immediately clip it to the black negative lead from the voltage meter. This should cause the generator to speed up and the reading on the voltage meter to steadily rise, topping out between 12 to 13 volts. If either fails to happen, the armature is starting to fail, and you should replace or rebuild the generator.

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