It has been debated whether or not an aftermarket stereo head unit can be used with the factory Bose amp and speakers, with no How-To or DIY to prove it, so I decided to take the challenge! About time I'm contributing something after gleaning so much valuable info from everyone here.
Here is the way I got it to work.
I went to Crutchfield.com to research and buy the hardware (No, I do not work for them). If you use them you can put in your vehicle (2004/5 Miata with Bose system, 4 inch tall factory radio) and it will suggest all of the necessary accessories you need as a kit for the MSM whenever you add a head unit in your cart. This kit also gives you a great discount on the accessories. The most important accessory for this to work with the factory Bose system is the Scosche SLC4 Line Output Converter. Again, these things can all be found elsewhere but Crutchfield makes it easy and cheap. (I like a simple receiver with Aux input and cd player. I dislike all the bells and whistles that I don’t use. If you get a really fancy receiver there may be additional wires and accessories required.) The main advantage to replacing the unit is that I now have an auxiliary-in plug that lets me easily connect my phone/mp3 player to listen to music. Plus I got a cubby for a little extra storage space. I also feel that the sound quality is better, but it is still a loud convertible with full FM exhaust, so how good can the sound quality get, right? All you lose is the factory/stock look and the 6 disc CD changer. This is a completely and easily reversible process, so the factory stereo can be put back in at any time, probably in less than 15 minutes.
Here is my order.
When you get your hardware, it is time to get it installed. First step is to remove the old factory stereo. If you have never installed an aftermarket head unit, get a friend to help you that has experience. It isn’t very difficult work if you take it step by step and read directions, but the wiring can be a little tedious if you have never done it before. Read the instructions for the wiring harnesses and read this How-To several times before getting started and make sure you understand what you are about to do.
Caution: You may want to disconnect your battery for this operation. You will be working with electronics. Also, not my responsibility if you break your car… blah blah… this is your fault if you mess something up.
Remove the covers on each side of the factory unit. I pried them off with a small screwdriver from the top, between the checkered surround and the top corner of the unit. Most people will probably use a plastic or rubber tool to avoid damaging anything.
After the covers are removed it will reveal 5 holes on each side of the unit. Using 4 removal tools, insert them into the bottom 4 holes on each side. You will hear a click when they are in far enough. You may have to wiggle them around a bit to seat them properly, then pull out on all four at once to pull the unit out.
The back of the unit has 2 connections – an antenna (black cable) and the stereo connector (white connector). Your unit may also have a 3rd connector for satellite radio or cassette deck. Mine did not so I’m not sure which it is. Remove all of these connections.
This is what it looks like when the unit is removed. The big white rectangle and silver pointy thing are the connections you removed.
I got a better picture of this, but couldn’t get it to upload. This is what the Scosche Line converter looks like wired up. The stereo wiring harness attaches to the input side and the Metra adapter wiring harness attaches to the output. The 4 stereo signals (left front, right front, left rear, right rear) go through this box. Connecting everything else isn’t very difficult – everything is color coded – but it can be tedious. Just connect the red to red, orange to orange, ect of the stereo harness to the adapter harness. Only caveat is to attach both the blue and blue/white stripe to the blue. Make sure all of these connections are solid as you will be stuffing all of these wires into a small space later (solder works best, but I just use twist and screw connectors. They have always worked for me on the stereos I have put in every car I’ve owned). I always do this on a table inside before I take everything out to the car. It is easier to take your time and do quality work. When you’re done wiring it up, make sure the switch on the left side is in the middle, on “Factory Amp”.
Once you have the wiring harnesses all connected with the Line Converter, connect the adapter side of the harness (the red/orange connector in my case) to the factory connector in the dash.
With it plugged in and the harness stuffed into the dash it will look like this.
Now connect your new head unit. This will not the final install so no need to make anything pretty. This will be a test fit. The other end of the wiring harness will go into the back of your unit as well as the antenna. I had to cut some electrical tape that was wrapped around the antenna wire to get more slack/reach.
Using a small screwdriver, turn all of the “Factory Amp Gain Adjustment” knobs (the ones closer to the output side) of the Scosche box completely in the “-“ direction (CCW) until they stop. Put your keys in the ignition and switch the ignition to accessory mode and turn on the stereo. Turn the volume up on the stereo to what will be your usual listening level (I turned mine to 25 out of 50) and tune to your favorite radio station or put in a good CD (using a CD is preferred as it will remove possible inconsistencies that occur from using a station with bad reception). Now return to the Scosche box and turn the same “Factory Amp Gain Adjustment” knobs in the “+” (CW) direction until each channel reaches your desired listening level. You may want to turn up each channel incrementally to get a feel for the volume of the whole system instead of turning one speaker up really loud first and it overpowering the others. I tried to turn both front channels the same amount and both rear channels the same. I took this opportunity to raise the volume of the rear channels slightly more than the front channels so that the windblocker speakers are a little more effective. I seem to be in the minority in that I can hear the windblocker speakers with the factory unit though, so this may not give you any better results. To me, it improved the WB speakers’ performance though. After you are satisfied with the balance of the sound, turn off the ignition and disconnect the stereo.
Now it is time to get the mounting frame ready to put in. I used this double DIN kit that adds a cubby slot for extra storage. The kit also came with a plate that has an opening instead of a cubby, which would work great for adding a few gauges above or below the head unit. The silver frame shown in this picture usually comes installed on the head unit. You will have to slide it off of the unit in order to mount it to the black plastic kit. Slide the metal frame in from the front and bend the tabs on all four sides as shown.
Now you can slide this into the opening in the dash where your old stereo was. You will hear a few positive snaps when it is in place. See a few pictures up for how I crammed all of the wiring into the opening before inserting the mounting frame in order to get it to all fit right. It is a tight fit! Make sure you grab the antenna and stereo harness connectors and have them accessible when the frame is snapped in place. You’ll need to attach them to the stereo later.
This kit can be installed with the head unit on top or on bottom, but I could not get the wiring to all fit and reach properly with the head unit on the bottom.
Plug the stereo wiring connector and antenna into the back of your head unit as you did when you were about to test it. This time it may be more difficult because the mounting frame gets in the way. Once it is all connected, slide the head unit back until you hear it click on each side.
You have installed a new stereo head unit! Turn on your car and enjoy the new sound and controls. I feel that the sound quality of the system is much
better with my new unit. The aux-in feature is the main reason I got the unit and makes everything much easier.
If something happens and you need to remove the head unit it is usually very simple. This may vary unit to unit, but most stereos I have had have been like this one. There will be two metal tools in the box that your unit came in that look this. Remove the surround around the face of the unit and insert one tool into the slot on each side of the unit as shown. When you hear a click for each side pull back on the tools and the unit should come free. Pull it out until you can disconnect the wires and free the unit.
