A lot of those cars have a changer option on the factory stereo which means an emulator can provide an aux input. There are some adapters on the commercial mar

A lot of those cars have a changer option on the factory stereo which means an emulator can provide an aux input. There are some adapters on the commercial market for this and lots of arduino-style projects published on the web. So far this year I built two such adapters for family and friends.