Bulb and wiring. Pull a bulb from your old headlight set and install it using the reverse of the removal method (there is a little hook to unhook the spring) I plugged the main plug to the bulb so it's always on on my naked; I didn't bother with the little running lights as I always want the headlight on. This bulb appears to be a double filament, so I suppose it's possible to get little creative and wire that second filament up if you wanted a hi-low beam etc. Maybe search the boards for this. Honestly, the single light sucks so bad I don't think I would want to ride at night with it other than down a freeway where other cars are lighting the road. I am a total lighting snob though so that's worth keeping that in mind as far as that comment goes. Or, you could probably mod this with a HID projector setup like other have mentioned. I don't plan to ride at night with this rig.