As you can see the image in my post#12, the led's PCB is quite small (narrow). It is ment to be put inside an existing stop-light case ("boītier" in french).

I haven't enough space to put either the µc nor the power regulator on the led's PCB; this is why I made a second PCB for the "power & µc section". It is located outside the stop-light (still inside the car but not inside the case).

Finally, and this is why this all is about, I wanted to reduce the amount of wires between those two PCBs.

Voilą.

Another general info: I made my second proto with 15° leds; this viewing angle is to small, 24° must be better.