bypass relay

looking for a bit of help. Installed a tow bar on my ml 250bluetech. I have got a bypass relay and wired up and the only thing I can’t get working is the brake lights any help would be appreated. Cheers

Hello all - new here and first post! Just purchased a 2013 B180 Diesel Sport with the 1.5 diesel, and I am going to add a tow bar this weekend. I am not going to use a dedicated wiring kit, but will use a SMART by-pass 7 way relay. My question is, what can I connect to for my main power supply...