The red banks break toggle switch on the dash let’s me turn it on and off. It does turn on for a couple of minutes at start up regardless of switch position to help keep from building up too much carbon in the system I think. It’s primary purpose is to slow down the truck and load when going downhills. Saves your breaks I’d assume and also keeps the load under control without having to use the breaks constantly in hilly areas. It usually doesn’t run when stopped except at start up. It seems to shut off around 10-15mph and start up when letting off the accelerator pedal over that speed.