If you have the 2 wires 30h and 50 (smaller start wire on wrong small terminal) mixed up you will get the starter spinning and not engaging but that wouldn't happen while the car was just sitting unless somebody is playing a prank on you.

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