I dont normaly bother to fit a rear brake light as i hardly ever use it.

If you really want to fit one and there isnt a place to attach the switch buy a pressure switch. It replaces the banjo bolt that goes into the master cylinder. When the brake lever is depressed the fluid pressure in the brake line operates the switch and the brake light comes on.

I think Goodridge sell then as do brembo. I have one fitted to the front brake on the RC as there is no where for a normal switch.
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If I have to take the carbs off once more...