IBM RT PC Options Installation page 127

3. Connect any cables you disconnected earlier. Then, to install the
rear cover, slide the cables into the slots in the cover.
a. Insert the bottom hooks into the holes.
b. Push down on the cover.
c. Insert the top clips into the loops.
4. Insert the key into the keylock and turn the key clockwise.
After you have installed the options, it is important to record
hardware changes on the record stored in the system. Verify the
Section 3. Installing Adapters in All Models 3-19