How to hook up a single wire brake light

Ok I just got two new controllers for my trike and the high brake wires which I thought were brake light wires only has 1 wire and its a ground wire where do I pull the hot wire from or just how do I wire up this single wire to a brake light.. Thanks so much Brian M.

That's not how that works.

Applying 12V to brake HI causes the Controller to either regen or just ignore the throttle input.
You need an existing 12V system just like on a motorcycle or car where it sends 12V to the brake lights... and the controller in this case.