Abstract: Control signals for electric consumers in vehicle doors and l.f. signals for loudspeakers in vehicle doors are transferred from a control apparatus (1) provided outside of the door over a common data line (42, 43) to a door module (20, 30). For this purpose, in the control apparatus (1) the control signals are modulated in binary-coded form onto a carrier signal and onto the same carrier signal there is also modulated the l.f. audio signal. In the door module 30) the signals are demodulated and separated according to frequency. The l.f. signals are amplified and fed to a loudspeaker (4, 5). The control signals are evaluated by a micro-controller (24, 34) and they control over switching stages (23, 33), setting elements (6, 7) provided in the door. Conversely there is also possible a data transfer from the door module (2, 3) to the control apparatus (1).