You are working in a pretty big can of worms there! First thing you need is a wiring schematic to follow, and then very likely a scan tool to diagnose/code the LCM (light control module) Are the replacement lights LEDs ?

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)