Trophy 1200 Alternator Connection Help Please

As part of my Trospeed project I am ripping out all of the old 1200's loom and replacing it with the brilliant (and tiny) Motogadget. Everything becomes soooo simple and straight forward until it comes to the alternator.
It is the lower spec, 25A unit and only has a twin bladed connector which powers everything - Brown & Black wires, with the earth being the alternator body. According to the Haynes bible, the brown goes (eventually) back to the +ve battery which makes perfect sense. The Black wire however looks like it powers another circuit entirely - mostly headlamps and other V+ related duties.
My question is, Should I simplify things and just use the Brown wire, leaving the black one redundant? Can I hook it up to a battery warning light or similar? (ok, that's 2 questions )
As usual, any help will be hugely appreciated.