alan, thx for the reply
in meantime, I re-purposed ca3.1wp (8-pin plug) orange wire (key return) into 'parallel' e-brake signal wire (re-soldered orange wire to e-brake 'blue' wire inside ca3), then in the trailer, wired 2 wires, one to the left edge e-motor blue wire (e-brake), the other to the right edge blue wire, connected to edge controller.
i used android app and bluetooth module, set regen brake setting to 50 (i guess %), and did a test ride - it worked, me happy
just, for my purpose, 50 % regen braking is way too much, I will set both to 20 % (minimum available), and test it; then, if needed, I will slowly increase the regen value
in my case, on trike, the tow vehicle, one brake lever is connected to (both) front archer drum brakes, while the other (left) brake lever is connected to physical brakes on trailer, and also as e-brake to ca3.1, and now also to both mp5 edge controllers (blue wire, for e-brake signal)
this basically means I am done with my trailer, I just need to mount solar panels, and off we go - into world adventure
thx for the input,
have fun
aum
ps: anybody interested, you can follow me on youtube - aum hren (chose the channel with 40+ videos)