If you want to play your iPhone's tunes on your car radio, you have several options, depending on the technological capacities of your car. If your stereo has an auxiliary, or AUX, port, you can use an auxiliary cable to connect your iPhone. If you have a tape deck, you can use a special cassette to play your iPhone's music. If your car has neither of these, or if you prefer a wireless approach, you can connect your iPhone to an FM transmitter.
Plug one end of an auxiliary cable into your iPhone's headphone jack. Plug the other end of the cable into your car's auxiliary port, which should be marked "AUX" and look like a 3-mm hole. Switch your radio's input to "AUX" -- just as you would switch from radio to CD. Turn your iPhone's volume to just below 50 percent. Open the iPod app. Tap the track you want to play, and once the song begins, adjust your stereo's volume accordingly.
Insert a cassette adapter into your car's tape deck if it has one. Plug the other end of the adapter into your iPhone's headphone jack. Set your radio's input to "Cassette" or "Tape." Turn your iPhone's volume down to below 50 percent. Open the iPod app and tap the song you want to play. Adjust your stereo's volume once the music starts.
Insert an FM transmitter into your iPhone's headphone jack. If the transmitter comes with an app, open it and select the option to scan for the best available frequency. If not, use your stereo's scrolling arrows to find a radio frequency without any extant station or interference. Set your FM transmitter to this frequency. Turn your iPhone's volume to below 50 percent, open the iPod app and tap the track you want to play. Once the song begins, adjust your stereo's volume accordingly.