Using original loom

I'm converting my series 2 to electronic. The loom is original and the scooter is a battery model. I want to power a 12v battery. The brake light switch is the 3 hole type. Am I right in thinking that I connect the red and grey wire in the loom to B+ on the regulator to trickle charge the battery and run the brake light and horn? Shall I also connect the brown and purple to G on the regulator to run the lights? Shall I connect the purple to the brake light switch bearing mind that the battery is also powering the brake light? I'm happy for the lights to be AC so I'm not looking for a full DC system I just want a battery for a single spot and DC brake light and horn would be a bonus. Ta for help.
Paul.
Paul.