...thanks for the info!

exactly... pin4 = positive pole (+5V; red cable); pin6 = ground (neutral; black cable);
Usually the fans make some noise (scratching...); here it helps (as mentioned elsewhere) to turn the fans upside down (i.e. they suck out the air instead of blowing it inwards...). They don't make noise any more (mine have become silent, so to speak...) AND you can feel whether warm or hot air is flowing out.

Thanks for the tip - I felt the same way. Delivery without instructions :-)

MVP

In this video, the connection of the fan can be seen better and is also explained:
https://m.youtube.com/watch