Left side is tractor of semi truck and right is back of semi trailer. On the back of trailer is levered switch that instantly turns on truck brakes when activated.
Backing into a dock or person standing behind truck pushes a lever and current to triggers brake valve assembly. Lamp in simulator lights to show air pressure in brake line dumped.
I am thinking this must be connected to truck emergency brakes. This second switch at back of semi trailer dumps air pressure holding brakes system open. One needs jumper around back switch so if you are backed into dock you can release emergency brake to pull out.
Precision stopping or positioning vehicles could use this method.
