Hello @cosimo_terzani. When you asked me if I was able to make the brake light mod it was on the second day of my first free days in a long time. But you ignited the realisation of it
Yesterday I made the connection in the 35 pin connector.
Kenneth suggested that pin #11 gives a 12V signal when regenerating. Then that signal can alert a relay which switches the brake lamp. (Edit: I was wrong with pin 11 giving 12V. See the remark of Kenneth below)
The wire to the brake lamp, GND and the 12V all can be accessed under the dash. From the switch on the brake pedal run four wires: GND; 12V; a fault signal and the brake light wire.
So the only job is to bring the wire from pin #11 to the dashboard and he rest can be found on the wires to the brake switch.
Bringing wire #11 towards the front of the car is rather easy when you remove most of the plastic parts around the left door and the long black plastic shield on the left underside.
Pull the wire horizontally through the left underside, next to the fat plastic cable bundle;
on the front side of that tunnel go to the inside towards the floor cavity under the lid in the footwell in front of the seat (where the handbrake cables split)
You see that on the left side of the footwell there is a vertical tunnel. Pull the wire through that tunnel from the front outside under the left headlight upwards, let it enter into the dashboard space from under the left square under the left headlamp and you have the wire where you want it.
I use these rods to do the job.
So far so good. Before realising the relay connections I checked the behavior of wire #11. It only gives some faint voltage, always below 1 V, even when regenerating at 500. It does not discriminate between accelleration and regeneration. The faint voltage drops when using the brake.
So I run into a problem and will not commence to connect the relay at this moment. Perhaps @kennethnilsen69 can help me out?