As far as setting up regen to Zero for trailing throttle, with full regen for braking adjustment,
there is a screw adjustment on the front lever. Just adjust the brake as loose as you feel comfortable,
the, adjust the screw to activate the brake light as early as you feel comfortable. I have mine set
VERY light. sometimes comes on and off with a very rough patch of road.
That being said, I don't believe that is what was being asked. If I am riding down the road, and, roll off
the throttle, it would be nice to have the light activate just from that action. Lots of electric cars got
rear ended early on because they were using regen without the brakes. Cars following didn't realize
that they were slowing down. I am guessing that some sort of additional switch and second light could
be set up so that when you roll off, the switch activates the second light. This way, the car behind
sees a brake light. Then, you can set your regen however you wish, independent of the second brake light.