My 2008 Hyundai Elantra GLS  had the AM/FM/XM/CD/MP3 radio with factory AUX input.  I wenr ahead and installed an aftermarket radio. I hate having things in my car not work, so I decided to figure out a way to keep the factory AUX input with an aftermarket radio, WITHOUT having to modify the existing AUX panel like another DIY I found here on the EC forums.

This is pretty simple to do, but requires simple modification of the Metra wiring harness..

[size=2]You&#39;ll need:[/size]

Aftermarket radio with AUX input, obviously
Dash Kit (I used the Metra dash kit found at a local car audio shop)
Metra wiring harness #70-1004
Small, thin screwdriver or thin ice pick / scratch awl
Solder, soldering iron
Electrical tape or heatshrink
3.5mm audio cable
Wire stripper

First things first, so we know what we&#39;re working with here.  Here&#39;s the factory pinout of the radio I had in the vehicle.  Noticed I&#39;ve highlighted certain pins.  These are the pins for the factory AUX input.  They&#39;re AUX L, AUX R, and AUX Ground.

http://www.lstwo.com/images/66445785874968620866.jpg

Here&#39;s before and after pics of the cable I used.  I just had this sitting around, and never used it, so I decided to just donate it to the project.  In the 2nd pic, you&#39;ll notice four wires.  There&#39;s a positive and a ground wire for each.  Left + ground, and Right + ground.  The grounds are the bare copper within each wire.  The sheathed wires are the positives.

http://www.lstwo.com/images/77407399692352494189.jpg

http://www.lstwo.com/images/25866166909079094703.jpg

Next I took the metra wiring harness, and modified it to fit my needs.  Luckily, there&#39;s 3 wires that happen to be in the metra harness that most of us won&#39;t need.  These three wires are the illumination wire, the remote amp turn on wire, and the power antenna wire.  Using your thin long screwdriver, ice pick, or scratch awl poke it inside the harness just above the wire you need, and push.  Then, pull the wire out from the back of the harness.  This should come out easily.  Try not to tug.  You&#39;ll remove the wire + the pin on the wire, which you can then just push through from the back into the harness on the proper pin you need for your AUX inputs.  Refer to the pinout in the first picture to see where you should locate the new wires.  Below is an image of the modified metra harness:

http://www.lstwo.com/images/14160811672806579913.jpg

Next we need to take your donor cable, twist the two grounds together, and strip a fair amount of insulation off the L and R wires.  Then attach them to the metra harness, making sure you hook the L to the AUX L, the R to the AUX R, and the two grounds to the AUX Ground.  For a good solid connection that will last years, take the time to solder them together, and then tape them off.  Here&#39;s a picture of the wires wired up, but not soldered yet:

http://www.lstwo.com/images/43975244431474611426.jpg

This next image shows my completed harness, with all wires soldered and taped properly, and then the harness taped to cut down on clutter and for easier install:

http://www.lstwo.com/images/50431520892809950917.jpg

And here&#39;s how the completed harness works with my Pioneer DEH-P6000 radio with rear aux input:

http://www.lstwo.com/images/50649945216752955953.jpg

Install the radio into the car, plug up all the harnesses, and bam, you&#39;re done&#33;  Your factory aux input still works perfectly&#33;