Brake master cylinders

[jappersx]

ive put a brake master cylinder on my cb500/4 from my cb650z and its fine apart from the brake light not coming on .light works ok with back brake peddle ,any clues as to what is going on

[Bryanj]

Nothing to do with master unless you bypassed the 3 way block bolted to the bottom yoke,
Front brake light on 500 is operated by a Hydraulic switch in the 3 way, sometimes the wires get disconnected when working on the bars

[SteveD CB500K0]

I assume that you added the poll by mistake so I deleted it.  If not the case let me know (sorry)