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Larry, Those coils labeled "12 volts for use with (or requires) an external ballast resistor" are in reality 6 volts coils and indeed on 12 volt tractors one is required or the coil will run too hot and the points burn up prematurely. That being said, the next question is WHAT OHMS BALLAST should be used????? It should generally be near the same ohms as the coils primary (measured between its lil + and - terminals) so a 50/50 12/6 voltage divider is formed. Typical of ballast ohms and 6 volt coil primary ohms would be maybe 1.25 to 2 ohms but ifffff ff the ballast is wayyyyy yyy higher in ohms then the coils primary, a low ignition current and resultant weak spark (especially when cranking) can happen!!!!! BOTTOM LINE you need the correct sized ohms ballast to match the coils primary winding resistance and most Ive seen are in the 1.5 to 1.85 or so ohms range ifffff fff designed for the old point n condensor ignition systems having coils of the primary resistance mentioned above. NEXT thing I would suspect is a bad/resistive ignition switch which a simple "hot wire" test will answer. Simply by pass eliminate the ignition switch by running a jumper wire direct from the hot ungrounded battery post to the high input (NOT to coil) side of the ballast n see what happens then????? ????? if that cures the problem suspect the switch. With the ignition on and the points closed (if all else is okay) when using a 6 volt coil and an external ballast on a 12 volt tractor there should be near 6 volts on the coils input but if its wayyyyy less suspect a bad switch or the ballast is tooooo o high ohms. FINALLY I like Olds suggestion,,,,, A weak battery and/or a weak starter can cause excess voltage drop while cranking which causes a weak spark which by passing the ballast could help (as a band aid approach). Have the battery load tested and if it and the cables n starter switch/solenoid are all okay but theres excess voltage drop on the battery while cranking, the starer could be the problem BUTTTTT T FIRST I would remove, clean n wire brush, n reattch each n every battery n starter switch/solenoid n starter n ground cable conenction cuz a bad cable or connection can cause voltage drop and a weak starting spark TRY THAT FIRST !!!!! !!!!! John T
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