brake lite switch with air brakes

If the brake and turn signal lamps are the same bulb then you may be able to get to the brake light signal at the turn signal control.

They make brake controllers that are actuated with air, they are made for your application.

DP's don't have brake light switches like you may be use to. You'll have to track your wiring down and find a place where you can tap into it. You'll often find the wiring you need near where your Allison computer, engine computer and other electrical is centrally located.

Usually there will be something marked in this area for brakes. Put a volt meter on it and see if you get 12 volts when the brake pedal is depressed with the ignition key ON.

Look at the foot valve, there usually a 2 wire switch on or near it. If not there, look for a air distribution block for the same type of switch. You will have to check it with a meter or continuity test light. If not on or near the foot valve, it could be a low air alarm switch.

check your fuse panel on my tradewinds (freightliner)there is a terminal marked for trailer brake