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A friend of mine asked me to look at this tractor because it would not start. My background is in auto repair. The engine turned over but no spark. The points would not open because the rubbing block was broken. I replaced the points and condenser and when I went to connect a battery charger I noticed he had installed the battery with the negative cable on the negative post of the battery. This tractor had a positive ground system. He had been trying to start this for weeks before I got involved. Did he damage anything by installing the battery backwards?

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  • Welcome to Motor Vehicle Maintenance & Repair! Does this mean he's been spinning the engine backwards? Nov 15, 2023 at 17:33

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If it wasn't running, there's not much chance that any harm was done. You don't say what machine, but the starter is most likely a series-wound motor, so the spin direction is always the same regardless of what polarity is feeding it. Likewise, the ignition system will run just fine with the polarity reversed, although the spark does jump the gap slightly better when the polarity of the coil is correct, but ironically this has nothing to do with the polarity feeding the ignition system, but instead depends on the internal wiring of the coil.

The only trouble might be if the engine starts and the charging system tries to charge the battery backward. But if the generator was appropriately polarized, even this should work just fine. Not sure how an alternator would handle this. Nothing else on a machine of this era should be harmed by reversed polarity. The ammeter would read backwards, though.

But what makes you think the battery was reversed? Even on a positive-ground system, the negative battery cable still goes to the negative battery post. And are you sure the machine wasn't converted to negative ground? Around here you find old tractors converted from 6V positive-ground with a generator to 12V negative-ground alternators all day long.

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