6.Locate the hard disk drive ribbon cable that you removed from the drive in the vertical mounting position. Follow the instructions below to attach the connector in the middle of this cable to the horizontal hard disk drive.
As shown below, there are two rows of holes in the connector. One of the holes is blocked with a plastic plug.
blocked hole
Notice the ribbon cable socket on the back of the drive; you see two rows of pins. In one of the rows, a pin is missing.
m&sing pin
Installing and Removing Drives