The OE hitch installation instructions are posted here under Online References. Those instructions cover the OE wiring kit.

You may not need coding depending on your year of manufacture. No info in your profile or sig.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue