Epson Progression U12 - Manual (Page 124)

4. If the drive you installed is the second hard disk drive (there
was already one installed), go to step 7.
If the drive you installed is the only hard disk drive, you need
to attach the hard disk drive ribbon cable to the main
system board. This flat cable came in the box with your
computer. It has three connectors: one on each end and one
in the middle, as shown below.
Locate this cable before you go to the next step.
5. The hard disk drive socket is located between the
subassembly and the CPU card socket on the main system
board, as shown below. (For clarity, the CPU card does not
appear in the illustration.)
CPU card
diskette drive
socket
subassembly
Installing and Removing Drives 4-21