@highlightmotor: These red and blue connectors are called GLADHANDS. They connect the service and emergency brakes from the truck to the trailer. The black rubber seals or “O Rings” prevent any air from escaping and allow the trailer’s brakes to work safely. It is important to ensure that they are always clean and in good condition, so our mechanics always routinely check and replace them when needed. See you on the road! #repairshop #truckmechanic #mechanic #gladhands #highlight