Epson 486SX - Manual (Page 126)

Changing the Jumper Settings
The hard disk drive jumpers are usually located on the drive’s
circuit board, near the large cable connector.
jumpers
The instructions in this section describe setting the jumpers on
the factory-installed hard disk drive. The jumpers on your
drive may be in a slightly different location, but you set them
the same way. See the documentation that came with your hard
disk drive for the proper settings.
7-4 Installing and Removing Drives