Hello, first post here, Q.
Where do I plug the 3 pin pump connector on this motherboard? All the fan and pump headers are 4 pin. I saw somewhere else that you can plug said 3 pin connector into any 4 pin header advice please.
Some Gigabyte boards have fan headers that can do either PWM or DC voltage control. If yours has this feature, you should be able to select Voltage mode (instead of PWM) for Fan Control in the BIOS. If your pump supports a range of speeds, you should also be able to set the speed you want in the BIOS or software application after selecting Voltage control. If your board only supports PWM, what Eddy said should work.
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".