When connecting the air lines (glad hands) between tractor and trailer, how do you prevent connecting them incorrectly?

GLAD HAND CONNECTIONS (air line couplers): The air lines connecting tractor and trailer are connected via glad hands. PREVENTING CROSS-CONNECTION: Often COLOR-CODED — BLUE = service line (control), RED = emergency line (supply); some are shape-coded or positioned to make incorrect connection difficult; many have different coupler designs; PROCEDURE: Clean the coupler/seals before connecting (dirt causes leaks); connect service-to-service and emergency-to-emergency; if there are no color codes, the emergency line couples to the emergency, etc. — connecting them backwards prevents proper brake operation; SECURE the connection (some lock); CHECK FOR LEAKS after connecting (listen, check air pressure drop); DEAD-END/DUMMY COUPLERS: When not connected, glad hands should be secured to dummy couplers or each other to keep dirt and moisture out; CROSS-CONNECTING the lines would cause the brakes to malfunction — a dangerous error; proper air line connection is part of the coupling procedure and is verified during inspection; always confirm correct connection and test the brakes before driving.