Credit for this write up goes to a member on seaclubgp.com. I will be doing this mod myself next month.
The $2.74 MP3 Jack For 2004 - 2008 Pontiac Grand Prix with XM Radio
Posted: Tue Apr 21, 2009 11:53 am • Rate Post
OK, you don't need XM Radio activiated for this modification to work. This allows you to add a 1/8" stereo jack that when plugged in, bypasses the XM radio signal and allows you to listen to a MP3 player, DVD player, etc. etc. through your stereo.
Here is what you need:
1) Radio Shack part number 274-264, 1/8" stereo headphone jack
3) Electrical tape or heat shrink tubing
4) Package of small wireties
5) Some small gauge hookup wire, 20 to 22 gauge will work best
Tools:
1) Wire cutter and stripper
2) Drill (darn it I don't remember the drill bit size) for one mounting hole
3) Kitchen butter knife
4) Soldering iron and solder
5) Phillips screw driver or small socket wrench set
STEP ONE: You need to remove the center stack cover from the dashboard. First, take a butter knife and pry off the trim ring around the ignition switch. Be careful not to scratch your dashboard. Second starting at the top, simply pry away the cover, it comes off easily. This exposes the air vent, your head unit, the climate control module and the storage bin. You can unplug your DIC without impact to the car.
STEP TWO: Remove the head unit, climate control module, and storage bin. All are held in by simple screws, easily done in just a few minutes. The way it is designed you can't remove the head unit without removing the entire stack, they lock into each other.
STEP THREE: Unplug the smaller 12 wire wiring harness from your head unit, this is the XM/auxilary connection into the stereo system. We're going to be cutting two wires and stripping some insulation from a third.
a) The brown/white wire is for the left audio channel - cut
b) The green/white wire is for the right audio channel - cut
c) The black/white wire is the ground wire - strip insulation to expose wire
Make sure that you don't cut too close to the plug so you have enough room to strip some wire and make the reconnection, at least one inch.
STEP FOUR: I found it was easier to build a wiring harness and solder it to the stereo jack and then splice it into the Grand Prix wiring, then trying to solder it all in the car. Using the numbers for the pin positions from the wiring diagram that comes with the jack from Radio Shack:
Pin 1: Common/Ground
Pin 2: Left INPUT
Pin 3: Left OUTPUT
Pin 4: Right OUTPUT
Pin 5: Right INPUT
I just soldered the connections on. The connections are very small on the jack so the smaller the gauge of the wire the better. I made the wire three feet long which was total overkill, but made it easy to mount. I then put wireties every 2 inches along the fire wires and snipped the ends off.
STEP FIVE: You're almost done, time to connect it all together
Pin 1 Wire: Connect to the stripped black/white common ground wire, solder or otherwise secure.
Pin 2: Connect to the RADIO SIDE of the wiring harness on the brown/white wire
Pin 3: Connect to the XM SIDE of the wiring harness on the brown/white wire
Pin 4: Connect to the XM SIDE of the wiring harness on the green/white wire
Pin 5: Connect to the RADIO SIDE of the wiring harness on the green/white wire
STEP SIX: Time to test! If you disconnected all connections to the stereo reconnect and put key in ignition to accessory. Make sure that your AM/FM, CD and XM radio still works. Check wiring if there is an issue. Set your radio to XM, XM does not need to be activated and it won't matter what station you're on if you did your wiring right. Now plug in an MP3 player, DVD player, etc, into the jack. Pick a song, you'll probably have to turn the volume up to get enough signal (I have a Zune and I have to set it to maximum volume to be equal to the XM level). TADA! You now have a successful input jack. Remove the plug and XM radio starts playing again.
STEP SEVEN: Mount the jack. I mounted mine to the right of the center air vent. There is a lot of empty space behind that part of the dash. I drilled a small 1/16" pilot hole and then drilled successively larger holes until I found the right size hole, testing each time, drill too big and the jack won't mount. Here actually is the hardest part. You're going to have to shave a bit of plastic from the interior side of the cover (the side you don't see) as the neck for the 1/8" jack is not long enough to get through the plastic and allow the mounting nut to grab onto the threads. I carefully shaved with a razor blade for about 20 minutes, checking as I went until I had enough thread for it to bite, and turn about two revolutions. Now just put everything back together. You should have a nice clean 1/8" stereo jack somewhere in your dash, otherwise it all looks stock and factory.
This modification works on almost all GM vehicles that have XM radio installed.
Hope everyone is well.
Thanks. I tore everything out today and had my homemade harness made, but it looks like it isn't gonna work? 
Originally Posted by RICHEYSGTP
[IMG]
