**Updated** Added 2NREATR's additional diagram and instructions to the bottom of this post. It seems about 50/50 for everyone as to which one is easier, so figured I'd combine them both.
And for those who don't know how to rep, here is a direct link:
If you plan to do this, read over the whole thing a couple times before you start......to make sure you are familiar with what each step involves. If there are any questions, feel free to post up.
I have refined the instructions for how to do this AUX input from others online, and made this specifically for the Trailblazer. It works on alot of XM equipped GM vehicles, that unfortunately do not have a factory aux input outlet.
First off, you'll need a few things. Most importantly, you'll need at least basic skills with soldering, as it will be the best method for attaching wires to the tiny pin terminals on the aux adapter.
1. At Radioshack, you'll need to get part #274-246. It'll likely be in one of the drawers in the electrical connector section. Ask for help to locate it easy. If you are on your own, the drawers are labelled by the first 3 numbers.....so look for drawer number 274.
2. The best wire to use for this is CAT5 cable, otherwise known as an ethernet cable......what you use at home to plug your modem and computer in with to get internet. If you plan to mount your aux input somewhere in the dash by the radio, a 3ft piece is plenty long enough. If you want to go into the center console or somewhere else, measure it out first...
3. You'll need some small wire strippers. CAP5 cable has 24ga wire, so your likely not going to have a pair that small laying around the garage. I made due with my strippers that go down to 22ga, but be very careful.
4. You'll need a #2 phillipshead screwdriver, and 7mm socket, and also a small flathead pocket screwdriver. If you have a small set of needlenose pliers, they will be of help too.
5. You'll need a good soldering iron and some thin solder. You'll also need to be at least decent at soldering, these wires/terminals are tiny. You don't want to heat the wire or the aux input too much, and you don't want to lay down too much solder.
6. Some electrical tape will help finish the harness up nicely, and I recommend some heat shrink tubing
Here is the plug from Radioshack. I put it on the TBSS keyfob to give you a size reference.
Here are the pin assignments on the aux input. It doesn't matter what color wires you choose in the CAT5 cable. I found the best method to be twisting the end of the wire good after stripping, and threading the wire through the tiny hole in the end of each pin on the aux input. I threaded it halfway through, then folded it back up and twisted. This provided a good hold until it was time to solder.
This is the end of the CAT5 cable. Just cut it off right behind the connector. On the end you choose to solder to the aux input, cut the sheathing down about 1-1.5" to give you some room to strip the wires.
My soldering iron......full of fuel and ready to be lit.....
All of the wires soldered on the aux input.
This step is very important. Write down what color wire you soldered to which pin. Do not forget to do this, otherwise you might as well just do this all in the dark. After you finish this step, and all 5 pins have wires soldered to them......cut the unused wire ends off. Now go to the other end of your CAT5 cable, and cut the sheathing back to expose 3-4 inches of the wires, and go ahead and cut the unused wires back from it also. It'll help you cut out alot of 'thinking' time when you go to solder up the other end.
After writing down your wire/pin assignments, now tape a 1/2" long piece of electrical tape.....and wrap it around each wire/pin....to cover the exposed area. Get it as close as you can to the aux input. All you need to do is wrap it around the pin, then sandwich the wire together. Do this for each pin.
You are now done with this part temporarily. Not get to your TB, and kneel down next to the passenger floorboard. Get a flashlight, and your 7mm socket. I used a drill, you can use whatever you want......but take out the two 7mm bolts that hold the kick panel in place. After they are out, there is a center clip that just pops out....pull it out with your hand.....
That square aluminum box mounted to the kickplate is the XM module. Here is a better picture of it.
Use a pair of needlenose pliers, and pry out each one of these clips that hold these electrical connectors in place. Do not disconnect any of these electrical plugs, yet.
Now the kickpanel will drop down out of place, and you only have two electrical connectors you need to unplug. Trace the bigger connector from the XM module, and you'll find one of the plugs you just removed from the kickpanel.......disconnect it there. It should be about 1ft long, from the second connector to the module. Then there is one mustard colored plug on the module. This plug is for the XM antenna. There is a thumb tab on the plug to depress, to pull the plug out of the module. You will likely not be able to execute this, its really hard to press. So take your thin bladed pocket screwdriver, and slip it into the tab and gently pry it up.....it'll release and you can slide that plug off.
Now you can take the kick panel inside your house.......with the 1ft harness still attached.....and solder this thing up in the comfort of your own home.
Disconnect the cable from the XM module. There is a blue tab in the plug.....slide it out, then you can depress the tab and pull the connector out. This will ensure you don't get the wires too hot when soldering, and fry the XM module.
This short harness has electrical tape on it. I found it easier to use the end of the harness away from the XM module (the more round connector, not the flat one). Make a small cut on the electrical tape, and peel the electrical tape back to expose a good 2-3 inches of wiring, as shown....
This is where you have a decision to make, which should be simple. With the way this was originally written......it is to eliminate the XM radio, since I am not subscribed. If you would like to retain XM function, look for the note in parenthesis below.
Now you need to pay attention closely again. For the wires from pins 2 & 3 (left side), you need to twist the stripped ends of those wires together. Now find the brown wire with the white stripe in the XM harness. Use a light....the brown wire really looks black. Make sure you have the brown wire.
From the connector, cut the wire about 2 inches. Solder the wires from pins 2 & 3 into this brown wire, that goes into the connector. Then take the wires you have going to pins 4 & 5 (right side speakers), and also twist those two together afer you have stripped them. On the XM harness, find the dark green wire with the white stripe. Also cut it about 2 inches from the connector, and solder the wires from pins 4 & 5 into that green wire. (if you wish to retain XM function, you need to connect the other end of the dark green/white and brown/white wire in with the harness for the AUX input....essentially you are then just adding the wires for the aux input to the respective wires for the XM speaker circuits......so you are adding those wires in just like is done for the ground)
The only thing left to do is to ground the harness. You now have one wire remaining in your CAT5 wire. On the end of the XM harness you are working with, you'll find the pins in the plastic connector are marked on each end.....with letters. You need to locate the black wire with the white stripe, that goes into pin "H" in your the connector. Be careful, there are two black wires with white stripes......make sure you are using the one into pin "H".
If you plan to use heatshrink tubing, obviously you'll need to slip it on the wire before you solder. Here are my wires soldering, with heatshrink melted in place.
To clean things up, now I wrapped the harness back up with electrical tape.....also to give the newly added CAT5 cable some stability with the factory harness.
Now, before you go further......test it out. Make sure you are plugged in at the module and on the other end of the XM harness. Make sure you have sound through both sides of the speakers.
You should have already planned where you want to mount the aux input. Take into consideration the depth of the threaded end. You'll need to find somewhere you can stick the male end of the input through, and manage to get the nut threaded on the outside. I chose to mount mine in the dashplate, beside both cigarette jacks.
I had to unbolt the knee bolster on the drivers side, and then had access to all the screws holding the entire dash faceplate on. It didn't take 5 minutes to do all of this, its not a big deal. Several 7mm bolts, and the dashplate is held in by about 7-8 phillips head screws.
I didn't need to take it all the way out to access where I wanted to mount it, this was enough......
If you want to take the trim panel all the way off to drill the aux port hole, more power to you. It isn't hard to get out. Just be mindful that its thin plastic, don't force it. I used a whale bone tool to pop out the trim around the cluster.....its non-marring. Just make sure you are conscious of what you use to pry as well.
To drill the hole in the dashplate, I used a Unitbit.
The thickness of that part of the dash is just a little too thick to just toss the aux input in and get the retaining nut on. If you choose this spot, you'll need to shave down the backside of where you drilled. The tool I used is a bit much, but it made quick work of it. This is a pneumatic grinder, with a bit used to grind metal with.
I can highlight it if need be, but here you can see where I shaved down the back of the plastic. It is 100% necessary to do, if you want to put your aux port here. It is necessary to get the outer ring on the port to lock it in place. You'll need tiny fingers or really small needle nose to get it started on the threads, and to get it tightened up some.
I took my time getting it shaved down the right amount, then put it all back together.......and it works great. CD quality sound too, couldn't be happier.
I had about a total of 1.25hrs in the whole process, but then again I turned wrenches for a living for 15 years. Just take your time with everything, it doesn't matter how long it takes you......what matters is this project is a success. This mod is WELL worth it......
Here is a video of my phone playing a song........if you have a sub on your computer, it'll sound like you are listening to the MP3 on your computer.
Originally Posted by 2NREATR
I have a few things to add too:
For those with XM bleeding through Ė the plug used in the write up (274-246) is called a switching plug. How it works is when nothing is plugged in it acts as a pass thru for what is hooked up to contacts 2 & 3 and 4 & 5. When you plug in your iPod (or whatever) it disrupts the connection between 2 & 3 and 4 & 5 therefore effectively disconnecting the XM. If you add in the wires from those tabs like you do the ground one, you are not utilizing the switching feature of the plug; you are just adding your iPod in to the XM signal.
If you donít care to keep XM you can use a simpler plug such as 274-249 from Radio Shack. Then you only need 3 conductors.
Enough with the words, the picture is way better!
I drew with the colors of wires used in the CAT5 cable. (I used 5 of the 8 conductors)
Picture of the real thing all soldered & ready for tape.
Hope this helps!