If your fault is the same as the video shown then it will be a short in the wiring in the tailgate hinge. If it is just when you accelerate it could be the wiring but it could also possibly be the latch that opens the glass rear hatch. They are both common failures with the E61. The latch is a cheap and relatively easy replacement, the wiring is a right pain in the tail..gate. There are guides on YT and forums on how to do it.