If it has an alternator, there would not be an external voltage regulator would it? Someone may have left an old regulator on it and bypassed it.
On the old tractors, I always use a one-wire GM alternator and strip out all the old wires and regulator and do a complete rewire. Fairly simple on old tractors, nothing to run except ignition and maybe lights.
NAPA has 12v coils with a built in resistor for the points.

Last edited by Old GMC Gold; 12/30/2013 10:19 PM. Reason: sp
57 GMC LCF 370
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2000 GMC 4x4
56 John Deere 420-W
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