Here are the Steps:
1. Buy a cassette adapter at your local Radio Shack or Best Buy store. They generally run about $15 dollars, and it's an easy way to have a good quality hookup to your car. You simply plug a standard plug into the earphone jack of your iPod, and a cord runs from that to a cassette which you place into the cassette player. Tune your car stereo to cassette, and you're ready to go (any cassette adapter at those stores should work with the iPod, so don't get suckered into buying the most expensive name brand). It is worth noting that the cassette tape is an analog medium, and therefore suffers some loss in audio quality.
2. Buy a wireless transmitter- these devices usually attach to your iPod, and require you to tune your radio to a designated FM frequency. While this is certainly the quickest and easiest fix, wireless transmitting has it's drawbacks. First, you will notice a slight decrease in your overall battery life. Second, FM radio transmissions do not usually exceed 96 Kbps, which means that any high-quality audio files (128 Kbps MP3 or higher, AAC, FLAC, MP4, etc...) are down-converted before being transmitted to the radio. This loss in quality is irrelevant to the untrained ear, but intermediate and advanced listeners may notice a drastic difference, especially on high-end stereos.
3. Try using RCA cables for better sound quality.
4. Remove the stereo from your dash. If it's a newer vehicle, you may need a special tool which usually just looks like 2 U's. The pointed ends are inserted into small holes on either side if the stereo. Pull the handles away from each other (pull the left one to the left, and the right one to the right). Pull, and the stereo will slide right out. If you have an older car, you will have to find out how to remove the dash and/or stereo. Sometimes it is just a couple of screws, and the rest is held on with clips. On others, you have to figure it out with trial and error (but remember, the more errors you make, the worse your car will probably look in the end). Ask some friends who may have the same car as you, or look it up online so it's done right.
5. Be sure that your stereo has some type of input in the back. If your stereo has a CD changer input in the rear with RCA inputs, you aren't out of luck - but you may be out another $50 because you need an adapter that changes the CD changer input into simple left and right RCA inputs. If you already have RCA inputs, there will be 2 of them (left and right audio). Usually, one is red, one is white, and they may or may not be covered by small rubber caps (depending on how old it is). If there are caps, you can remove them.
6. Decide where you will be putting your iPod and where you want the wire going. Once you've done this, drill your hole. For a way to make sure the wire never falls through the hole (forcing you to take everything apart to get it), go to step 7. Otherwise, skip to step 8.
7. If its RCA then the RCA to 1/8th inch jack should be fine, get an extension for the 1/8th inch if you need it but don't go splicing wires! Don't drill any holes; instead, find a way to run the cable under the dash.
8. Check that everything works, which usually requires switching to an "input" mode or "auxiliary" mode on your stereo. If it works, you're all set. Replace your stereo and dash. You're done.
Reminder: Check if there are no metal is exposed on the wires when you're done. If yes, removed or do it again because it will damage your iPod, car stereo or both.
Source: wikihow.com
