I... have..a plan...

So long as you drop the voltage from the white wire. You can't hook it up directly or you'll pop those lights in a jiffy.

the proper way to do it would be to use a voltage regulator. It's really not to hard to build, but I've built a lot of circuits so maybe im biased. The easy way is to use a resistor, you can find the value with ohms law V=IR. I is current, v voltage, r resistance. I can figure it out later after classes today if you like

White wire puts out AC voltage, at about 6VAC@3 W (3 to 9 depending on RPM if I remember correctly).

I forgot that it was AC. Works with incandescent bulbs. LED's are supposed to use DC.
so you need a 6 ohm resistor (that's tiny!) To drop the 3 volts if you pull all 500mA. But the spark plug may not have reliable sparks if you pull to much. You need to find out how much current the lights you have pull to figure out the actual correct resistor. You could do so but putting two double A batteries in series, putting a multimeter in series after the battery and before the light.

if you want to convert to DC. You can get a rectifier or make it out of diodes. That will drop your voltage some though. Which may be a good thing.

I plan on doing some things with the white wire and have it basically serve as the alternator portion of the engine. It's going to be difficult for you to run lights off of the white wire just because it changes throughout the rpm ranges. when I get my bike down here i'll be seeing what I can do with it. Shouldn't be to hard to build a current limited power supply to charge a 6 volt battery. Im surprised I haven't seen it here. Maybe I haven't looked hard enough yet