I have been getting a lot of PMs about how I got my navigation to work in conjuction with my aftermarket radio, and also keep my steering wheel controls(audio,talk/back), I will just post a thread so I can refer anyone back here when they ask about it.
First, lets explain the steering wheel buttons.
Take a look at this wiring diagram I found in this forum courtesy of Princess
Those are all the wires that come out from the back of the stock radio(navi or non-navi). As you can see in the pins 3 and 11, those are the wire signals that go from the steering wheel audio control buttons to the stock radio. Also, pins 12 and 13 are wire signals from the talk and back buttons. One look at the aftermarket harness from scosche or metra, and you can see that pins for those are MISSING on the harness. What you will need to do is basically somehow make a connection in the empty pin sockets. Easiest thing to do is probably to find a spare harness somewhere and extract the pins out of there(make sure to identify if its male or female pins). Use those pins and place it in the corresponding placement for the steering wheel controls as indicated in the wiring diagram.
This is an example of the work you will need to do:
However I also heard from user Janos about this harness: http://www.carxtc.com/servlet/the-21...X-Radio/Detail
supposedly its an identical replica of the OEM harness so it should already have the pins for the steering wheel controls and maybe the talk/back buttons. If that is true, it will be easier to buy one of those and start working on that one because it comes with more pins already.
So there, that should cover WHY it doesn't work and what you will need to do to get it working again....On the same note, you can also buy one of those steering wheel audio control adapters and tap into those same wires and connect it to your aftermarket radio to control that instead.
Now, lets go into how to make the stock headunit play sound after installing an aftermarket headunit.
Look back at the harness connecting into the stock headunit. Previously you have saw that it doesn't have any pins for the steering wheel buttons, but take another look and you will also see that it does not have any wires for speaker output! This is why your stock headunit cannot play any sound.
Now, there is more than one way to do this. You can buy a harness from metra part #71-1721 which is the harness that goes into the back of the headunit, or you can use the harness I posted above: http://www.carxtc.com/servlet/the-21...X-Radio/Detail
With either of these harnesses, you will have the speaker wire pins coming out from the back of the headunit, which you can use in any way you want. What I did was use a Hi/low converter from sonicelectronix($5) to convert the stock headunit signal to a low level rca signal. Most hi/low converters can input 2 channels, so I took the front left and front right(makes the most sense). I then bought a RCA to 3.5mm aux converter cable to change the rca output to a commonly used 3.5mm aux line found on ALL aftermarket radios.
This is the Hi/Low converter I got: http://www.sonicelectronix.com/item_...o+Adapter.html
and this is the RCA to 3.5mm aux converter cable I got: http://www.monoprice.com/products/pr...seq=1&format=2
Plug the 3.5mm end into your aftermarket radio so whenever you switch to the AUX input, you can hear the stock radio play again!
This is a picture of how clean it can look, just have the 3.5mm cable coming out through the hole in the dash kit:
Hope this write-up will help out many audio system builders!