The purpose of the ballast resistor is to drop sufficient voltage (often 12 down to 6) so the coil only draws its rated current and dont overheat and likewise the points switch whatever current they are rated to handle so they dont burn up prematurely.....
The ballast should be sized so it drops enough voltage such that the remaining voltage is what the coil is rated for. Typically that would be 12 volts down to 6 so if the coils primary is 1.5 ohms the ballast would also be around 1.5 ohms for a 50/50 voltage divider. If you have a 6 volt coil measure its primary resistance (between its lil + and - terminals) and the ballast would be near the same and typical ones are in the 1.25 to 2 ohm range
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Today's Featured Article - Good As New - by Bill Goodwin. In the summer of 1995, my father, Russ Goodwin, and I acquired the 1945 Farmall B that my grandfather used as an overseer on a farm in Waynesboro, Georgia. After my grandfather’s death in 1955, J.P. Rollins, son of the landowner, used the tractor. In the winter 1985, while in his possession the engine block cracked and was unrepairable. He had told my father
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