Epson EQUITY 3865X/20 PLUS - Manual (Page 174)

4. Align the ribbon cable connector with the socket on the
hard disk drive. Make sure the row in the connector with
the blocked hole lines up with the row in the socket with
the missing pin, as shown below.
missing pin
hole
Make sure the holes fit over all the pins
and
then push the
connector onto the pins.
Caution
If you do not correctly align the holes with the pins, you
could severely damage your hard disk drive when you
push in the connector.
Now go to the next section for instructions on connecting the
power cable.
7-30
Installing and Removing
Disk Drives