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.

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.

Erase Jumper: Used to erase the firmware