Epson EQUITY 386SX/16 PLUS - Manual (Page 172)

Align the connector with the socket so that the row in
the connector with the blocked hole lines up with the
row in the socket with the missing pin, as shown below.
Make sure the holes fit over all the pins and then push in
the connector.
If you will have two hard disk drives in your system,
perform the procedures in steps 6 and 7 again. This time,
however, attach the connector in the
middle of the
ribbon cable to the horizontally mounted hard disk drive
you just installed. (If necessary, turn the subassembly
upside down to make it easier to connect the cable.)
B - 3 8
Installing and Removing Disk Drives