I measured drive connector on the back of the Amiga and got 4.95v on the 5v-pin and 11.84v on the 12v-pin, so I guess that's fine.
The external drive has a 26 pin floppy connector while the internal drive has a 34 pin connector, so I won't be able to swap them around for testing purposes.
I guess I could measure the external drive itself, but I'm not sure where 5v, GND and 12v is located:

As for the motor sounds; it can be heard in the clip in the first post (
here), does it sound normal? When the drive is empty the humming (audible in the video) stops, and the drive makes the ticking sound (as normal) while waiting for a disk. The ticking sound is louder in the internal drive, but I guess that can vary from drive to drive?
Perhaps this is a dumb question, but I think this is the motor:) - and I am able to turn it manually with ease, so I guess it is not seized?:

Edit:
I unscrewed the motor to be able to flip it around and get a better look when using the drive. I could see that it was spinning without any problem. However, I noticed that the belt seemed a bit loose, and may not be tight enough to be able to get any traction off the motor. I stoumbled upon a couple of threads
talking about the RF-332 cases with Citizen drives (which I have), and it seems that people are having to replace old belts in these types of drives.
The belt is barely moving when the drive is trying to read a disk, so I guess this could be the issue?
Thanks!