If the factory-fitted OEM radio in a vehicle controlled by CAN bus is to be replaced by a retrofit radio, a specific CAN bus adapter is required. specific and universal CAN bus adapters convert relevant digital data from the respective vehicle-specific data bus into analogue signals. Depending on the adapter, various signals or comfort functions such as ignition plus, lighting, reverse gear signal or even a speed signal are read out and made available in analogue form for various retrofit solutions.