It depends on the options your e53 left the factory with. I have the Professional CD and MID in the dash (SA663) and a 6 CD-Changer in the trunk (SA672) so there are zero speakers wires rear of the B pillars. Nada.

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Wayne
2005 BMW X5 3.0d (b 02/05)
2001 BMW F650GS Dakar (b 06/01)