Apple PC Compatibility Card - Manual (Page 13)

13 Installing the Card in a Power Macintosh 4400 or 7220
13 Disconnect the other end of the audio cable from the Macintosh logic board, and remove
it from the computer.
This cable is connected near the DRAM DIMM slots. The connector has four
pins and may be labeled “CD AUDIO” on the board.
Be sure to pull on the plug, not the cable. After you have disconnected the
cable, carefully remove it from the computer. (Keep this cable; you will need
to reinstall it if you ever remove your PC Compatibility Card.)