Asus RS720-E7/RS12 - Manual (Page 62)

4-10 Chapter 4: Motherboard information
5. CPU, front and rear fan connectors
(4-pin CPU_FAN1-2, FRNT_FAN1–4, REAR_FAN1-2)
The fan connectors support cooling fans. Connect the fan cables to the fan
connectors on the motherboard, ensuring that the black wire of each cable
matches the ground pin of the connector.
• DO NOT forget to connect the fan cables to the fan connectors. Insufficient
air flow inside the system may damage the motherboard components.
• These are not jumpers! DO NOT place jumper caps on the fan connectors!
• All fans feature the ASUS Fan Speed Control technology.