Brown Wire and Tail Light Lit Fork Lock Position
Apparently in Europe, if you park your bike on the side of the road, it must have a light on the front AND on back of the bike. Therefore, most European bikes use the brown wire to light a peanut bulb in the headlight reflector or a very low-wattage element in the headlight. It has to be switched on.
Many American riders use this "always on" wire to power an accessory device. Otherwise, it is firmly connected to nothing and you should ensure it doesn't intermittently connect to something.
The tail light fork lock position on the ignition switch provides power to the tail light and locks the fork. Most Americans only find this feature useful in determining how long it takes to unknowingly drain the bike's battery down to nothing. This feature is useful in developing the skills necessary to push-start the bike.