Well you can find many different 12-volt adaptors to power an iPhone. But that is for power, not playing through the car speakers. For that you need a connection through the car stereo system. Some systems have dock connectors that will both power your iPhone and play the music over the car's speakers. Others just take a stereo jack input and will play the music. Either way it is something you have to get for your car. You can't just do it with an iphone accessory.
Go to a local car accessory store and ask them for help with options.
Well you can find many different 12-volt adaptors to power an iPhone. But that is for power, not playing through the car speakers. For that you need a connection through the car stereo system. Some systems have dock connectors that will both power your iPhone and play the music over the car's speakers. Others just take a stereo jack input and will play the music. Either way it is something you have to get for your car. You can't just do it with an iphone accessory.
Go to a local car accessory store and ask them for help with options.