WARNING: This page is about a different car, the 2005 BMW 530i, 2005 BMW 525i, 2004 BMW 530i, and 2004 BMW 525i. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Wiring Diagram Charging System 525i & 530i (1 Of 2)
Courtesy of BMW OF NORTH AMERICA, INC.
Fig 2: Wiring Diagram Charging System 525i & 530i (2 Of 2)