[New2DMax]

Just a couple of ideas.
Mine has a wire from the harness that tells the controller that the truck brakes are active. I believe this is off of the third brake light switch. Mine changes color on the indicator light when I touch the brake if everything is hooked up and adjusted correctly. I also have a level control selector. This determines how agressively your brakes react. My book says to have the arrow pointing straight down with trailer on, for a good starting point. If this is too far forward, the brakes may never engage because it doesn't think you need it. If the slide works, then the gain is working.