The Gateway 500 is capable to work as a media player (Gateway music functions are active). In order to make it run with the current car, you need to set the switches according to the current car. The exact DIP switch settings are in the install manual.
There are 6 DIP switches on the bottom of the Gateway. Switches #1-4 are for setting the car configuration (Mercedes, BMW, Audi, Porsche and others). DIP #5 is not used.
Turning on DIP switch #6 deactivates the CD changer side optical connector of the Gateway 500. This can be used if the car has no CD changer.
After changing the switches, you need to turn off the whole car with closed doors for 10 minutes to finalize this new setting.