Abstract: An assembly unit for the interior finishing of passenger carrying vehicles, in particular of two story railroad car type, consists of modular prefabricated functional units each having at least one of the functions cable duct, loudspeaker, illumination, baggage repository, window shade, and interior covering. Support beams of the functional units are suitably designed aluminum extrusions. The prefabrication of the functional modules takes place outside of the car body in a workshop region specially equipped for this purpose and comprises the working procedures, mechanical processing, surface treatment, assembly of the functional devices, prewiring and functional testing. The functional modules are installed and assembled in a predetermined sequence in the car body into an assembly unit containing the named functions.