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