Epson EL 3S/33 - Manual (Page 65)

6. Position
the power supply cable connector so that its
notched comers line up with the notched comers of the
power supply connector on the hard disk drive.
notched
7. Make sure the holes fit over all the pins and then push in the
connector.
Caution
If you do not align the cable connector correctly, you could
severely damage your hard disk drive when you push it in.
4-6 Installing and
Removing Drives