what i did with my yz426f is bought ufo head light,add-on tailight/brake light w/lic.plate holder found the smallest gel cell street bike battery i could find, mounted it to top of the air box (it hangs down inside)hooked up the head light and taillight through a switch so i can turn them off/on,then hooked the brake light up through a hydraulic switch on the rear m/c directly to the battery so it comes on when i put on the rear brakes on all the time, i did this because we some times get on the road to connect trails and if there are any police i may stand a better chance of getting away with it if i have a brake light.where i live it's very easy to get a regular title for dirtbikes and get plates so i am some what should i say legal.i do have to charge the battery pretty often if i run all the lights to long but i mainly use the head/taillight to pass tech inspection then turn them off leaving only the brake light to drain the battery when the brakes are on just an idea it works for me.
later
jeff