This question has generated great debate on the forum in the past.
Using the power wire from any 6 volt china girl or HT engine to power a usable head light will take power from the ignition.
Lets face it, 6 volt systems on the market today are not capable for sustained use at high RPM, 6 volt bulbs will burn out quickly or rob enough power from the ignition to make the engine miss and run poorly.
I've built a stand alone 12 volt recharging system, using a 12v wheel generator thats been adapted to run off the shift kits jack shaft, a small gel type12 volt motorcycle battery (these are cool because you can mount them on there sides) with a simple charging/alternator circuit built in.
As the bike runs at speed with its lights on the generator feeds the lighting system, then as the bike slows down it switches over to the battery.
I use one 12 volt, 35 watt, truck fog light as my main head light and two 6 volt LED small but bright white flashlights as distance and "curb"lights.
In the rear, wired to my brake lever I use two of the same flashlights with red filters.
The LED flash lights have all been wired together so I can kill the lights if need be.
Your system need not be as complicated as mine, you could just run one white head light and one red tail light off a 12 volt rechargeable battery.
Hers a few picks of my light bar just for inspiration, I hope this helps.
Please feel free to ask any questions if you need assistance.