Ask the Mechanic

Polarizing the Generator

(Progressive Farmer image by Steve Thompson)

READER: I need some help with the charging on my John Deere model B tractor. It has electric start, and the generator won't charge the battery. I was told that I need to polarize the generator to make it charge. My question is how to polarize the generator. The tractor is a positive ground, and I don't know if it would be polarized differently if it were a negative ground like some other tractors that I own. Can you lead me through the steps to polarize the generator? I just had the generator and regulator repaired, and have a new battery in the tractor.

STEVE: What you will be doing is polarizing the generator so it knows if your tractor is a positive or negative ground. That way, it knows how to charge your battery. This is a simple job. First, go ahead and install the battery, generator and regulator. Next, take a short wire and touch across the A terminal on the generator and the BAT terminal on the regulator. Touch the wire on both terminals very quickly. You should see a spark. That's it. You are ready to go. If you need to polarize a negative ground generator system, you do exactly the same thing.


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