Add a dashboard jack for your car stereo’s rear aux input

When I bought my car, one of the first things I did was buy a fancy new Alpine head unit to replace the factory stereo. This gave me the ability to add an XM tuner and an iPod adapter. I ran the iPod cable into the glove compartment, so I could just connect the iPod in there and close the glove box when I hopped in the car.

This was pretty sweet. Between XM (BPM and The System mostly, since you asked) and my iPod, I never had to suffer through a commercial in the car again.

Then I, upon receiving instructions from Steve, went out and bought an iPhone.

That's now the iPod that I use most of the time. Strictly speaking, though, the glove compartment isn't the most useful place for one's phone (though it could be in the top 10). And, to boot, when I attached the iPod cable from the stereo to the iPhone, the screen cleared and just said “accessory attached”. Not terribly useful.

So, I decided I'd add an aux input to the radio, and hook it up to the iPhone's headphone jack. That part was easy; since I had an Alpine head unit, all I had to do was buy a $20 cable and attach it to the existing “AI-Net” bus. This gave me a pair of RCA-style connectors behind my radio.

Well, that project was far too straightforward and had little to no chance of inflicting significant damage rendering my vehicle undriveable, grotesque, or en fuego. I decided what I really needed was a jack on my dashboard so I could plug the iPhone in there, and wouldn't have an ugly cable crawling out from some dusty crevice in my dash. That would give the project the professional look that I want deserve pine for.


If you want to follow along, here is the stuff you'll need:

  1. A soldering iron (with solder, nimrod)
  2. A headphone extension cable (or any other stereo audio cable with a 1/8″ plug and a female connector on one end) such as this one
  3. A 1/8″ 3-conductor (stereo) jack, such as Radio Shack part 274-249
  4. A 1/8″ 3-conductor (stereo) to dual RCA cable, such as this one

The Plan

So, here's what we'll do:

  • Mount the jack in a convenient location in the dash area of the car.
  • Cut the extension cable and solder the female end to the connectors on the back of the jack.
  • Use the 1/8″ to dual RCA cable as-is, connected to the RCA female inputs on the head unit.
  • Then, connect the male 1/8″ plug from that cable to the female 1/8″ connector attached to the jack, and we'll be done!

When we're all finished, we'll be able to pump our awesome tunes through our car stereo, and look like smooth and sophisticated as we do it. 'Cause that's just the way we roll.

Note: I'll show you pictures of how things looked around my radio, but you'll be on your own to find a good, convenient spot to mount the jack. I highly recommend using a Crutchfield Mastersheet for your vehicle if you're not familiar with accessing the area behind your radio. I don't know that you can buy the Mastersheet by itself, so you might have to buy something else to get it. It won't be hard to find something you want.

Another note: Be careful. There are wires behind your dash, and some of them carry scary, impish little beasties called electrons that would love nothing better than to zap you and ruin your day. Don't give them the satisfaction.

Step 1: Rip stuff apart

First, I opened the dash according to the Mastersheet instructions to expose the aux input jack that I had attached to my head unit.

Aux input jacks; do not taunt

Step 2: Burn yourself with the soldering iron

Next, I went to my workbench to build the jack that I would install later.
Out of the box, the jack has three connections on the back–one each for left, right, and ground. On the back of the box, there's a helpful diagram that shows how the connections match up to the conductors on the inside. This diagram is not terribly helpful. Based on that diagram and some independent research, I've labeled the jack a little more clearly so you can see the purpose of each of the conductors in our project.

Connection diagram for the audio jack

Take your extension cable, and cut it a few inches behind the female connector. Inside it, there should be three wires, which will eventually match up with the three solder points on the jack. Usually there will be a red wire for the right audio channel, a black wire for the left audio channel, and a bare wire for the ground. You'll need to strip the outer covering of the wire for some length (maybe about an inch and a half) to expose the inner wires, then strip off about a half-inch from the shielding on the inner wires.

The end of the split cable

So, ok, it's time to solder. This involves a power tool, so you should feel good about yourself as you do it.

If you need an intro to soldering, you can find those on the web pretty easily. The only thing I'll say about the topic is that, if you need to buy a soldering iron, you should get one that uses butane fuel, like this one:

Butane soldering iron; totally 1337

In my opinion, these are better because you're not tethered to an electrical outlet, and they heat up faster than the cheap electrical soldering irons that I've used before. You can buy the butane fuel in the tools area of a hardware store for a few bucks. Plus, it's powered by FIRE! And fire is cool.

Anyhoo, attach the wires to the appropriate conductors and apply the solder. Once you're done, you should have something that looks like this, but maybe a little better since I just kinda learned how to solder on my own:

Wires soldered to conductors on the jack

After the solder cools, you should wrap a bit of electrical tape around the left and right conductors to make sure you don't get a short. If you had more foresight than me, or if you're reading this before actually doing it (ha!), you could also thread some heat shrink onto the wire before you solder, and then just move it into place and heat it up. But I didn't think of that at the time, so bah.

After you tape it up, it will look like this:

All taped up

At this point, you have done all of the electrical work. This would be a good time to test it out. If you have headphones and a 1/8″ stereo patch cable, you can attach one to each end of the device you've assembled (one to the end of the cord, and one to the jack), and then the extra male connector to some audio device, like your iPod, or a can of tuna. If you hear music through the headphones, that's a Good ThingTM. If not, then check your soldering to see if you have a loose connection.

Even if works just fine, bend the wire gently (not hard!) to see if it affects the sound. If it does, then you should check your connections and resolder. If not, then you totally rock.

Step 3: Mounting the jack

The next part is going to be highly specific to the vehicle you're installing the jack in, so I can't do much more than provide a case study of what I found. You need to find a spot in your dashboard, preferably on a piece that you can temporarily remove, that is thin enough and has enough room behind it to accommodate the back of the jack.

In my case, there was a spot right next to the radio that suited my needs just fine. The area surrounding my head unit is actually removable, so it was easy to take it over to my workbench. I originally was going to use a spot lower on the console near the gear shift, but ultimately decided against it since it was not removable, and thus much harder to access.

A couple other things to consider in selecting a spot: Give some consideration to how you'll run the wire from the aux input on the back of the radio to the installed jack. You'll make your life easier if you minimize the amount of cable fishing you have to do. Also, remember that you'll be plugging a wire into the front of this jack and running it to your portable device. I chose to put the jack on the right hand side of the radio instead of the left so the wire wouldn't obscure my view of the radio's display.

Next comes the big scary part: drilling the hole.

I started by removing the metal mounting collar from the jack (very important!), and choosing a bit that was obviously slightly smaller than the part that pushes through the hole. After taking a few nips of brandy, I drilled that small hole all the way through. I then repeatedly increased the size of the bit in 1/64″ increments and redrilled, until the jack would push through. I'm not going to lie to you, this was nerve-racking. It was difficult to get past the “ZOMG I'M DRILLING A HOLE IN MY CAR ZOMG” feeling, but I did it, and that means you can, too.

In my particular case, when the hole was large enough for the jack to fit through, I found that the plastic was slightly too thick so the threads on the front weren't quite exposed enough. The mounting ring couldn't grip them! To save the day, I broke out a Dremel with a grinder attachment and slightly deepened the hole on the back of the panel so the jack would poke though a little farther in the front, allowing the mounting ring to grip the threads. I also had to grind a little bit of the trim so the square backing of the jack would fit properly, but I was careful to only grind the inside edge so it wouldn't show once it was installed.

Grinding down parts of your car. Not scary at all.

Once I was done grinding, though, it fit just fine, and as you can see, the jack fit nice and flush against the back.

Aw, yeah.

The threads poked through in front, and the mounting ring grabbed them to hold the jack tight:

View from the front

Once the grinding was done, it looked like this:


Step 4: Hook it up

I just had to connect the wires and reinstall the panel in the vehicle to be all done.

It was a simple matter to attach the 1/8″ to dual-RCA cable to the female 1/8″ plug that I had just installed:

RCA cable attached

From there, I took the whole assembly back to the car, and connected the RCA cables as appropriate:

Everything connected

If you're following along at home, it's a good idea to test your setup at this point before your car is all put back together, so you don't have to take everything BACK apart if you have problems. If you connect your audio source to the jack with a patch cable and turn on your radio, it should work! If it doesn't, check your connections and go backwards, a step at a time, until you find the problem.

In my case, things worked just fine, so I put my car back together and admired my expert craftsmanship.

…and there was much rejoicing

Step 5: Drink heavily

And you're done! Now, when you've ripped your favorite music to your iPhone and you're jonesing bad in the car, you have a solution that doesn't compromise your style. And, it's pretty awesome to be able to put that patch cable away when you don't need it.

If you decide to do this project yourself, let me know how it goes in the comments!

PS: If you decide to buy something from Crutchfield as a result of this post, and you're a new customer, hook a brotha' up and give them referral code “p51zi-fiv3b-gx3yu”; you and I will each get a $20 credit. That's cool.

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