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Stephen, when you convert from 6 to 12 volts you need to do EITHER in the ignition system: A) Keep the old 6 volt coil but add an external voltage dropping (12 to 6) external ballast resistor in series after the ignition switch and before the coil, or B) Use a new full true 12 volt (internally ballasted) coil in which case DO NOT use any external series ballast resistor. Many full true 12 volt coils are labeled "12 volts" or "12 volts NOT for use with external ballast" Many 6 volt coils are labeled "6 volts" or "12 volts requires external ballast" If in doubt use an ohmmeter to measure the coils primary winding resistance between its lil + and - terminals. A 6 volt coil will be in the vicinty of 1.5 ohms while a 12 volt would be more like 3 ohms. The typical ballast resistor would be around 1.5 to 1.85 ohms power rated in the vicinity of 20 to 30 or so watts, many are ceramic wirewound bathtub style. If you use an unballasted 6 volt coil at 12 volts it will get so hot you can barely hold your hand on it plus the points will burn up prematurely and the coil may overheat and fry. The ballast is available at Tractor Supply or Rural King or NAPA etc and so are full true 12 volt coils which require NO ballast Post back any questions John T
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