Plug and socket devices for measuring and diagnostic purposes are known in the art. The substantial disadvantage of said plug and socket devices is that they only furnish mechanical and electrical connections. For diagnostic purposes, an additional socket for connecting the corresponding diagnostic device must therefore be provided. According to the invention, in order to provide for automatic diagnosis when the plug and socket device is connected, the latter has insulation piercing connectors, screw terminals or spring terminals for connecting at least one cable. A printed circuit board, on which a diagnostic and evaluation circuit is located is provided in the housing of the plug and socket device, at least one switchable terminating resistor is provided and the plug and socket device has a display device that is connected to the diagnostic and evaluation circuit for automatic continuous display of evaluation results. The device is applicable in the domain of connecting devices for bus systems and networks in data systems and communications, as well as for computer and automated systems.