I may have confused a few people, so let me try to explain a few things.
By override switch, I meant the same thing you are talking about, a manual switch. I can press mine part of the way down and get partial voltage sent back to the brakes, or I can press it all the way down, sending 100% of the voltage back to the brakes. When I was testing my brakes, that is how I was doing it, I was pressing this button all the way down to make sure I had good brakes on the trailer. One of the wheels locked up, and the other didn't.
Paul