I'm using a MBP with a German keyboard. However, as you probably know, it is an annoying layout. Therefore, I use the normal US layout instead. This, however, was not enough. The upper left key (right below the ESC) originally maps to § and ±. Therefore, using karabiner I remapped it and checked Swap tilde with section. This now works as I want on the internal keyboard.
The problem is that when I attach an external native US apple keyboard, the upper left key is mapped to § and ±. Is there a way to disable karabiner on the external keyboard? Any other idea?