a green wire sticking out from under the fly wheel that is connected to a magneto. The rectifier is connected to that. It's the reason the light gets brighter at higher rpm because all it does is rectifie the AC produced by the Magneto to DC. The voltage is not stabilized by a battery. A magneto is just a cool of wire rotated between two magnets that produced an alternating pulse (AC) via a cam operated switch. Most of the older Yamaha Enduro models and some of the sport models came with the Magneto installed but I'm not sure in the new models have it. Just look and see if you have the wire. Some engine manufacturers provide it as an option which can be retrofitted.