[rotorwrench]

The diode in that kit will kill half of the AC wave for a half wave AC which is like a pulsating direct current. The bulb kills off some of the extra voltage since I think the Model T magneto can generate up to near 28 volts. It's not ideal but it will function. The battery might get overcharged to a certain degree. If it's a sealed one, it might not last as long as intended but it would charge it. A diode bridge with a Zener diode dump would likely do a better job if it is correct with the end result parameters.