First verify from BMW or stereo folks that it's in that location. (that's where it's at in most) If it is in rear post, rear seat has to be removed & weatherstrip and a few screws & the interior cover panel comes off. Then it's just a visual inspection - you'll probably see a wire hanging off or just loose. It's simple once you get to it. (another good source would be check with a Best Buy car stereo installion facility - they're good at shating info)