I retrofitted both my E39 and E53 with BT. On my X5, the mic wire was not present where it should be. My dealership explained that the factory will sometimes leave the wire hidden up in the headliner, they pulled it down for me and I completed the install.

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2011 550xi Carbon Black/Oyster, M-Sport, Premium Package, Technology Package, Electronic Damper Control, Dynamic Drive, Comfort Access, Active Seats, Surround Cameras

2013 X5 5.0 Space Grey/Black, M-Sport, Premium Package, Technology Package, Comfort Access, Surround Cameras