By TE Connectivity AMP Connectors 72
TE Connectivity's MU connectors include a 27-pin receptacle, plug, and “dummy” receptacle that is used to convey the locomotive functions between units. The 27-point trainline connectors allow a single point in the train to issue up to twenty-seven commands to all or some of the vehicles simultaneously.
TE’s MU27P connectors are used to convey control and indication signals such as door controls and indications, brake applied and released indications, and public address as well as audio and other passenger rail functions. These connectors are designed to accept three 10 AWG leads with all other leads being 12 AWG or 14 AWG, which allows them to be completely interchangeable and intermateable with other brands adhering to the AAR-S-512 specification, and are key in preventing intermating of different wiring configurations.