Make sure your jumpers are set correctly.

V_FAN: This is where you select the voltage for the 5 fan ports. You want the jumper on VIN (pins 2 & 3) to set the fans to run on the voltage that is supplied to the Duet 2 WiFi(24v). If you set it to 5v(pins 1 & 2) the fans won't turn on.

5v Selection: You need to select if 5v is provided by the onboard regulator(24v to 5v) or from an external 5v source.

Only use INT 5V EN or EXT 5V EN.

INT 5V EN: Most builds you will have the jumper placed here.

EXT 5V EN: Place a jumper here if you want to use an external PSU to provide 5v to the board.

If desired you need to connect the external 5v source to the +5V and GND pins on EXT 5V header

Erase Jumper: Used to erase the firmware