Epson 386/25 - Manual (Page 233)

7. Now connect the hard disk drive cable. As shown below,
there is a tab on one side of the connector, just like the
diskette drive connector. The hard disk drive socket at the
front of the main system board also has a notch on one side.
hard disk drive connector
tab
hard disk drive socket
notch
Align the connector with the socket so the tab on the
connector lines up with the notch in the socket. Make sure
the holes in the connector fit over ail of the pins in the
socket and then push in the connector.
Caution
If you do not correctly align the holes with the pins, you
could severely damage your computer when you push in
the connector.
Installing and Removing Disk Drives B-53