Originally Posted by johnracer

or, it could be to engage reverse without starting the delay box timers. The timers start with the release of the trans brake button. If you have a pro brake, you'll need to push the tb button to back up. The 3rd button could be wired into a diode to bypass the box........

By the way, most starting enhancers come on with the application of the trans brake and don't have a special button.
Johnny