Check the truck out a bit closer, especially the tranny part. Either that switch is for a brake line lock or a trans brake. We need a bit more info after you check it out. If it a line lock, it's a simple solenoided system to hold front brake preesure to start a burn out or even help hold the car at the line while you ready it for launch. If its a trans brake set up, it holds reverse against first until the light turns green and releases the reverse hold.