Epson Progression U12 - Manual (Page 114)

3. If you are connecting a hard disk drive, locate the hard disk
drive ribbon cable. It is a flat cable with a red wire running
down one side. (If you are installing your second drive, one
end of the cable is connected to the main system board and
another connector is already attached to the hard disk drive
in the internal drive bay. Use the free connector for the
second drive.)
The connector has two rows of holes designed to fit over the
pins in the drive socket. The red wire on the cable helps you
orient the cable connector to the drive. Align the connector
with the socket so the side of the cable with the red wire
faces the power supply socket on the drive.
Make sure the holes fit over all the pins and then push in the
Connector.
could severely damage your drive when you push in the
Installing and Removing Drives 4-11