Connection device for data communication between two vehicles

The connection device comprises a data line (11,21) and two plug connections, which are connected to the data line and are assigned to different conduction paths. A data splitter (12,22) is provided between the data line and the plug connections. The data splitter checks the plugged in plug connection that is connected to the corresponding plug connection, and activates the assigned conduction path. One of the conduction paths is activated when both plug connections are used. An independent claim is included for a method for establishing or for operating a connection for data communication between two vehicles, particularly between a towing vehicle and a trailer vehicle.