The Br/W also powers the Br wire to the taillight through the ignition, so you will have to account for that if you want a taillight. The switch provides power from red to black, then b powers Br/w inside the headlight bucket and the Br/w runs back to the switch to power the br. Neither circuit, br/w and Br, will be complete without the switch. You'll have to power them another way.
Yeah, I took one apart. Just because.
Patrick