my '72 GMC has a black and red button for tractor protection and a red one for parking, it also has the hand valve for controlling the trailer brakes. usually when the brakes apply themselves it is because the air pressure gets too low, most trucks have buzzer that turns on when the pressure drops below 60 psi so you still have some time to stop and wait for the pressure to build back up. you get used to them after a while.
