Epson 386/25 - Manual (Page 225)

The interface that protrudes from the back of the drive has
gold contacts on both sides. Near one end of the interface,
there is a gap to accommodate the plastic divider on the
connector.
Align the connector with the interface so that the plastic
divider on the connector lines up with the gap in-the
interface, as shown below.
divider gap
Make sure the cable connector fits properly onto the drive
interface and then push it onto the interface.
Caution
If you do not correctly align the connector, you could
severely damage your diskette drive when you push it in.
If you removed a hard disk drive from the vertical mounting
position, go to step 6. If you did not, go to step 8 for
instructions on connecting the power cable.
Installing and
Removing Disk Drives
B-37