There was no set standard for diesel MU connections until the late 1960's, when everyone basically adopted the EMD arrangement. Even then many newer units had 2 MU plugs, including a 27 pin socket to operate ' field loop ' dynamic brakes on older units. Some Espee passenger F - Units had an extra MU plug allowing them to MU with Alco PA's. For years Baldwin diesels used compressed air to operate ALL MU functions, which resulted in a bunch of air hose connections on each end of all units. This feature also prevented Baldwins from operating in MU with diesels of other builders. The small air hoses visible on the end pilots of older diesels supplied compressed air to the locomotive sanders; this function is now controlled electrically.