Okay, as promised...
Ive meassured the stop/brakelight and there is voltage on the stop light 3.5v even when not engaged. So, im told that I need a DC 12V contact relay to put in between, 3 wire, whereas one wire goes to power and the other two goes from brakelight and diode at the speedo....
I just dont know how to source such switch in English, so if anyone could find the right Words for this and shoot me a message ill appreciate that
something like this "potential free make contact"