A 2-pin fan can run on a 3-pin header by making sure the right connection between the supply line and the ground connection.
2 Pin Fan to 3 Pin Header
If you’re wondering whether running a 3-pin fan on a 2-pin connector is possible or not, the answer is yes. The objective of the third pin on a fan header is ‘sense’, and its job is to see how fast a fan is spinning. So it’s only needed on one of the fans on the splitter, not all.
However, as it can’t measure three fans at the same time and how fast they are running, you can only plug in the fan one way because of the plastic ‘guard’ on the fan connector and header.
How To Connect 2 Pin Fan to 3 Pin Header
Now the question is, which of the three pins should you connect to the 2-pin connector? You have to connect the +12V and GND and leave the rest alone. Red and black wires should be the power and ground and the blue/yellow wire will be the PWM (Pulse-width modulation) line. If that does not work, try the red and the other one.
Anyway, the 2-pin configuration has no way to send out a speed signal, so you cannot check the speed of such a fan. A 3-pin fan is generally connected to a mobo fan port and the speed is changed by changing the supply voltage on the mobo port. The third pin of the adapter cable is connected usually to a yellow/blue wire to the fan.
What is the difference between a 2-pin and 3-pin fan?
A 2-pin fan does not offer the rpm measuring feature of the CPU fans. While the third pin of the 3 pin fan allows to send out a speed signal with the output of the built-in ‘Hall Sensor’ chip. The third wire, a monitoring circuit can display the rotation.
Long story short, it is possible to run a 2-pin fan to a 3-pin header by connecting the two wires to the live and neutral prongs of the 3-prong plug. For color-coded wires, make sure to join live to the live terminal and neutral to the neutral terminals.