Apple iMac G5, 20-inch - Manual (Page 213)

iMac G5 (20-inch) Take Apart - Lower Fan
Replacing the Lower Fan
1. With the midplane assembly positioned over the edge of the table, align the fan screw
holes with the matching holes on the chassis. Replace the fan screws.
2. Turn over the computer assembly and route the fan cable through its cable guides.
Connect the fan cable to the connector on the logic board.
3. Replace the midplane.
4. Replace the back cover.