Tailgate pushbutton, outside tailgate
WARNING: This page is about a different car, the 2013 BMW X5, 2012 BMW X5, and 2011 BMW X5. However, it is still accessible from the selected car via links, so may be relevant.
The tailgate pushbutton switches to earth. The signal of the tailgate pushbutton is picked up by the junction box electronics. The junction box electronics signal the status of the tailgate pushbutton via the K-CAN to the HKL.