I second Crassius's point. You can use the White Wire to power a light but.... you will lose out on engine power and it could potentially screw up ignition timing. Some newer engines don't even come with the White Wire. Mine didn't.
If you want to add a light, go with a battery powered one that has an on/off switch.
My instruction book for the install gives specifications for the generator white wire output. Says it will provide 1/2 amp at 7 1/2 volts. This is way more than enough for a couple of LED headlights. I will go out on a limb and say that is not DC however, so if using a LED lamp you may want to use a rectifier (diode) to make DC out of it as LED's typically have a very low tolerance for reverse voltage. Since there seems to be no real standard for these things your results may vary. I have a few of what Ebay calls Buck Regulator which basically take anything from 3 to 30 volts in and output whatever you set for the output, so I may try that just for fun to get a regulated output for a LED light. Larry
The bridge rectifier will work if there is not a common ground from the mag to the light. One side of the generator in the bike is tied to the frame so the light must not have one side also tied to ground or the bridge rectifier will basically short one polarity of the AC output to ground. Likely not a problem with the new LED lights, but if you look at a drawing you can see that having two common grounds (one on the generator and one on the light) will not work with a bridge type rectifier. Larry