An iPod is playable through your car's amp using an auxiliary connection, so if no sound is heard after hooking it up, there is a problem to be discovered. The solution can be simple if you know where to look. At the very least, you will be able to narrow down and isolate the problems by going through a rudimentary step-by-step process that will likely end up fixing the problem altogether.
Press play on the iPod. The song will start and the progress bar will start moving forward. In addition, the "Play" symbol (the triangle) will be displayed next to the track, as opposed to the "Pause" symbol (the two vertical lines). If no sound is heard, move on to Step Three. If the iPod screen is frozen, move on to Step Two.
Reset the iPod. For the classic iPod or the iPod Nano, simultaneously hold down the centre button (the circle in the middle of the control wheel -- it will be the same colour as the body of the iPod) and the "Menu" button (the top of the control wheel) until the iPod turns off. For an iPod Touch, press and hold the "Sleep/Wake" button on the screen until a virtual slider appears on screen that reads "Slide to Power Off." Slide the slider to turn the iPod touch off. Restart the iPod (regardless of version) and press play. It should start without any problem. If there is still no sound, move on to Step Three.
Press the "Aux" or "Auxiliary" button on your car. If the iPod is plugged in and playing (as evidenced by the progress bar on the screen advancing), your car stereo may not be on the proper input. If your car does not have an auxiliary input and you have a connector that plays through the radio, check to make sure the radio and the connector are tuned to a station that does not get a signal in your area. If you try to play the iPod through your car's amp via a station with a strong signal, you will hear the station's broadcast as opposed to your iPod. If the problem still persists, move on to Step Four.
Check the connection on both the iPod and the car's auxiliary input. If the jack is not inserted completely into either end, no sound will come from your car's amp. If everything is connected properly and still no sound is coming from the radio, continue to Step Five.
Test your iPod by listening to it through either headphones or a docking station. If it plays with no problems, the problem lies with your connector and you should continue to Step Six. If the iPod does not play, there is likely an internal problem which will necessitate a visit to an Apple Store to have it repaired.
Replace the connector. If everything else on your iPod and your car's amp is working properly, there is likely a faulty connector. You can pick up a new one at most electronics stores, ranging in price from £9 to £32.