Fan not spinning up after replacement

I was working on replacing the loud and old fan on my iMac G4. I cut off the connector of the old fan, and determined the polarity as follows:

Cable color iMac → corresponding cable on replacement fan (Arctic F9):

Black → striped black cable

Red → middle cable

Yellow → outer black cable (not striped)

When connecting the old fan like this to a USB adapter, it spins up. Installed in the iMac, the new fan doesn‘t spin up and isn‘t „detected“ by the OS (10.4.11). How can i go about testing the polarity of my cables is correct? I do have a multimeter available, i just don‘t know what to measure.