It's the bigger plug that clips to the side of the fan shroud. The little plug should go to the f.auc sensor (senses air pollution and switches to recirculate).

12V on the big plug is neccesary but doesn't tell the whole story. The other wires are ground and a pulse-width modulated speed signal that the fans digital electronics decode. Not a "dumb" 0v = off, 12v = full on sort of thing.

If you have the software, you should be able to activate the fan manually and see if it runs.

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David.X5
2001 X5 4.4i Sport
SOLD! at 160k miles