Apple PC Serial and Parallel Card - Manual (Page 55)

Opening the computer
1 If your computer is turned on, shut it down and wait 20 minutes.
Before proceeding with these instructions, you need to allow the computer’s
internal components to cool.
2 Disconnect all the cables from the computer, including the power cord.
Remove the power cord now so you don’t pull it by accident as you turn
the computer on its side in the next step. You’ll reconnect the power cord in
step 4.
55 Installing the Card in a Power Macintosh 8600 or 9600