Thysanoptera is on the right track.
Some of these AIO coolers use a Y-splitter so the AIO CLC pump and fan use just one motherboard header instead of multiple headers.
On the Y-splitter if one male plug has four pins and the other has three pins, pair the four-pin connector with the fan. That will let the mobo control the radiator fan speed via PWM. The three-pin connector is likely just wired to provide power (+12V, -12V, GND). In that case the AIO pump is intended to run at full speed.
Also, look at your motherboard's user manual carefully. Some motherboards have fan headers that provide different amounts of power. Look at all of the various cooling devices you have and plug the one that draws the most power into the header that provides the most power regardless of how it is named. On my MSI mobo I have five fan headers:
- CPU_FAN1: 2A, 24W
- PUMP_FAN1: 3A, 36W
- SYS_FAN1: 1A, 12W
- SYS_FAN2: 1A, 12W
- SYS_FAN3: 1A, 12W
Thus the 240mm AIO radiator pump plugs into PUMP_FAN1; this is configured in the BIOS to run at 100% regardless of the temperature. The two 120mm radiator fans use a Y-splitter and are connected to CPU_FAN1.
Cooling devices like ordinary case fans can go on the regular fan headers. If you run out of headers, use a Y-splitter for the case fans. In my micro-ATX build, there are two identical Noctua exhaust fans on the case top. I use a Noctua Y-splitter so the mobo only needs to control the speed of one fan, the other will run at the same speed (SYS_FAN1).
SYS_FAN2 is for the GPU AIO radiator fan and SYS_FAN3 is for the GPU VRM fan. All of my fan headers are fully utilized so the GPU radiator pump is gets its power directly from the PSU and runs at 100% speed all the time.