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Originally Posted by DHZIEMAN
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On this link, Randy Rundle has you set the VOM to the highest voltage range, but he does not say to use a DC range, not an AC range. You MUST use a DC range for this.
The actual difference between a coil for negative ground systems and positive ground systems rests upon which terminal the secondary winding returns to. When the points open and the coils magnetic field collapses, the secondary reaches a very high induced voltage. But,so does the primary winding. In the case of the correct coil for the polarity of the car, the primary's induced voltage adds to that of the secondary. If miss matched, the primary's induced voltage fights the secondary induced voltage.
It is easy to meter a coil and see which it s, but requires a very sensitive meter, as the ratio of primary to secondary winding is very large. I suppose no one wanted to know any of that, just spend the $10 or less on a new one and be sure.