You should be able to plug it into the fan header labeled "SYS_FAN3_PUMP". Even though it has 4 pins, the 3-pin female connector on your pump should still orient the correct way, leaving one pin out in the open. The header has an indented slot for the connector: both a 3-pin and 4-pin connector will only fit one way, so you should be able to easily attach that 3-pin connector onto the left 3 pins. Because the header is labeled "SYS_FAN3_PUMP" it leads me to believe that 1) you can either run a fan on it or a pump, and 2) your BIOS could be already set up or could be changed to run both PWM and DC fans at that header. Have you already tried it there? It also looks like that's the designated header on your mobo for a pump. No other fan headers are labeled "PUMP".