This aux-in trickery is designed for cars that have factory stereos with CD changer inputs. If your car has a CD changer, or the ability to hook one up, then you can hack into this input and use it for the iPod. If you don't have this option in your car, then I'm sorry, you'll have to move along.

The details of this mod differ with each car and each stereo, but the basic concept is the same: The CD changer is usually an outboard audio device that connects to the main head unit via a thick DIN cable. The head unit sees the CD changer as a "source" of audio. The thick DIN cable that connects the CD changer (oftentimes mounted in the truck/hatch/boot of the car) contains a lot of wires - data, power, ground, left and right audio... It is the two audio wires that we're interested in. You splice an additional set of wires into the audio L and R that are going to the head unit. The iPod then uses these extra wires that you've spliced in to play music to the car's head unit. Mount a double-pole, double-throw (DPDT) switch to control which music source (the CD changer or the iPod) you want to listen to.

Basically, you're tricking the car's stereo because it still thinks that you're listening to the CD changer even when you're listening to the iPod. If you car doesn't have a CD changer, but it has the ability to hook one up, then you can skip the DPDT switch and just use the DIN cable to feed the iPod.

Most of the parts you'll need can be sourced from Radio Shack or an electronics/hardware store.

There are a lot of pitfalls that you should know about before attempting this surgery to your car. First, you have to locate the DIN cable if your car even has one. If you've got a CD changer then you've got the cable and it's just a matter of finding where it's run (usually under the carpeting along one side of the car). You might have to remove some trim, part of the dash, a kick panel, or even a seat to get at it. Even if your car doesn't have a CD changer, if it was available as an option you might still have the cable. That sounds strange I know, but it is often easier for the manufacturer to install the cable in all cars during assembly whether or not the CD changer will be installed down the line or later at the dealer. If there is no cable, and you've verified this, then you'll have to buy the cable. These cables are specific to your car and your stereo, and while I'm sure there is some overlap with models, etc., you'll have to find out which cable is for your car and where you can buy it. If you can get it anywhere but the dealer, you're better off because they usually charge a lot for these (like $70 for my Saab!)

In addition, you'll need to be able to remove the stereo and inevitably part of the dash. This is usually pretty easy, but if you've never done something like that before you might want some help from an experienced friend/spouse. You'll have to very carefully cut in the DIN cable and wires. Soldering the connections is the best way to do it, but sometimes just a good solid crimp will do.

I can't tell you the details about how to do this to your car, and I can't be held responsible for anything you do while working on your car after you drink those beers. The best place for more car-specific information is a forum dedicated to your make or model. Some of those guys on the forums are nutso when it comes to their cars, and a search through the forum (try "aux" or "ipod" first) can sometimes get good results. I've found two good DIY pages, one for Saabs and one for VWs, that can get you started. They also show some pictures so you can visualize the steps that I've talked about. Feel free to add links to more DIY Aux In pages for other car models in the comments section.

Sean's Saab Auxiliary Input

Cristiana's Volkswagen New Beetle switchable AUX audio input