I did not try the applying the brakes manually with the brake controller. No need to as we were only going 45 miles per hour on a flat surface and the truck breaks were enough to bring us to a safe stop, although I had to put my foot all the way to the floor. I did not try increasing the gain as it was set at 2.0 which is more than enough to work. Again, what caused my truck brakes to fail? My truck brakes work fine as soon as I disconnect the trailer. Never had this problem before in 10 years of towing.