Hello there Carol,
I found an article named iOS: Troubleshooting car stereo connections that may just get that show on the road, so to speak.
Find it here: http://support.apple.com/kb/TS3581
1. Verify compatibility
Contact the manufacturer or refer to your car stereo's user guide to see if your device is compatible.
Note: Some accessories may have limited compatibility. See About iPhone and iPod accessories or About iPad accessories for more information.
2. Update software and firmware if necessary
Verify that both your car stereo and your device have the latest software versions. Contact the manufacturer to see if any updates are available. If your device does not have the latest version of the iOS, update to the latest software version.
3. Connect your device
Verify that your device is on and has music content.
Connect your device to the cable that came with your car stereo. For stereos that offer both a USB port and a 30-pin connector or Lightning connector:
Try the cable that came with your car first if your device has a 30-pin connector
Try the USB port first if your device has a Lightning connector
Note: Some car stereos are not designed to be controlled by Apple devices. When possible, use the controls on the stereo or steering wheel.
There are more tips down the bottom of the page, but these should get you started.