1 COIL FOR 6 AND 12 VOLTS

Usually, there is a slip of paper someplace that sez: must use with resistor. Well guess what?, read between the lines. Its a real 6 volt coil that requires a 12-6 dropping resistor to use on a 12 volt system. And since I'm assuming your NAA is still 6 volts, I'd install it bare foot.

And yes you are correct about the turns ratio. Primary is about 100 turns and 2nd is about 10K turns. But you're compairing AC transformer theory to DC inductive reluctance. But since you really using the collasp of the magnetic field of the ignition core by opening the points to generate the sparkies high voltage, it becomes a self governing scheame. ..... ....Dell

Unfortunately, there is no eazy shadetree mechanic test for designed coil operating voltages but you can kinda guess if the coil's primary winding is about 3 ohms, its a 6 volter and if its about 6 ohms, its a 12 volter. And of course, if its designed to be used with a ballast resistor, its got differnt resistances. So without having the ignition coil mfg specs, its hard to give definative advice. Leave alone the very technical problems of measuring low ohms.

Unfortunately, ignition coil manufacturers haven't found out about permanent lableing like paint, silkscreen or molded numbers. You get 'em in a box or throw-away bubble pack...dumb..... ....Dell