Question When coupling a trailer: Answers Make sure to couple the proper glad hands. Glad hands can be connected to any other glad hands. Only one set of glad hands should be connected. Explanation When coupling, make sure you couple matching glad hands. They are often color-coded to help drivers avoid mistakes. Typically, blue is used for service lines and red is used for emergency lines. Take a FREE Practice Test Now This questions appears in the following tests: Idaho Tank , South Dakota Tank , Alaska Combination , Arizona Combination , Connecticut Combination , New Mexico Combination , Vermont Combination , Virginia Combination ,