Hi nickjs,
I'm not the same page regarding regen with second throttle. I might know how to do it but just theoretically. Never did so yet. I've no diagram but I can write in words if it helps.
There is such wire marked with 'Brake'. I think this is signal wire. I'm might be wrong but as far as my electrical understanding goes:
Basically throttle has three wires:
-red, 5volts - this is power wire to feed throttle, - power source wire,
-black, 0volts, this is ground wire,
-white or yellow or green, is signal wire. This is the wire which "tells" controller how fast to spin motor or initiate regen in your case.
So you need to feed second throttle, therefore feed 5volts to red wire; connect black wire to ground; connect white/yellow/green wire to 'brake' - regen braking connection.
Set regen on the controller side through sabvoton app;