I got mine from a local electronic shop. It controls a front 120mm and rear 120mm fan. Basically the gizmo works like so. There are 3 tabs on the back, the 2 sides ones are the red wire IN from the fan, the middle one is the red OUT to power plug (they can be reversed but the general concept is the same. I love my reostat, helps keep the noise down. Now to work on my semi loud fish pump........