Ah Peter giving you the run around.
The fan spins freely cause the bushings are completely worn out. You need a new fan motor I had the same problem last fall.
I have a used fan if you don't want to pay the 200+ for a new one
But I could be wrong and you may have a messed up wire or problem inside your fuse box.
E30 Stuff For Sale: Clutch Fan and Shroud, 4 Pack Ignition Coils, ATE 750il MC (New), Offset Trailing Arm Bushings, m42 Valve Cover (Clean), M10 Engine Mounts (New), M42 Injectors,