That's it exactly. In older model MBs, like my previous 2010 E class, there were seperate feeds for each light function, L turn. R turn, Brake Light, Park Light, Fog Light etc. But in the 2014 Eclass, there is only one feed to the rear lamps for both Brake and Tail lights. When you press the brake pedal, it sends an increased pulse ( if thats the right word.. ) to the LED's, causing them to brighten. But for the 3rd brake light in the rear window, it has only a single feed. That's why I need to take the brake light feed trigger from there, and I'll use the Nr plate light feed as trigger for the relay for the park lights on the trailer. Problem is identifying which connection from the SAM or harness feeds the window brake light, thereby avoiding removing the rear seats and trims, including disturbing the AirBags. I'll be able to identify the Nr plate light feed easily enough, so it's not a problem.
