Mosfet Power controller

Hi

I just connected a mosfet power controller

robotshop.com/ca/en/mosfet-power-controller.html

to an arduino uno.

It looks like only 1 wire is needed to control it from the arduino. So we connected the arduino via the yellow wire to the side marked " IN". Tried both the + and - .

Problem is that the power stays on any way and we cannot shut it off.

My son has a 6V lantern battery powering a small Dc fan connected via the red and black wires.

Are we connecting it properly ??

I think you also need to connect the IN- to the GND of your Arduino.