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I finally got around to adding an aux in to my oem mk2 stereo so thought I'd write a how to as it's and easy and cheap mod which many could benefit from.

Disclaimer: if you follow this guide and screw up your stereo don't come crying to me, do this at your own risk.

What: the standard mk2/2.5 stereo is a modular system which can include combinations of cd, tape, multichanger and minidisk but has no aux in for phone/mp3 etc. This guide shows you how to add one.

Why: when aftermarket options are relatively cheap this is a valid question. I went down this route because...
- I'm going for an oem+ look
- This stereo only cost me £2.20 on eBay so figured it was worth the risk
- The mod cost me £1.50 and took about an hour, plus a bit of research time

References and background reading (where I got the idea and info from) ;)

What will you need...
- Small Philips head screwdriver
- 10mm socket (optional)
- Soldering iron and solder
- The aux lead of your choice (3.5mm jack or female equivalent, old pair of headphones etc)
- Stereo removal keys (not 100% necessary)
- A cd of silence (see below)
- Hot glue gun (optional)

The principle of the process:
Basically what we are doing is hijacking the analogue signal from the cd unit to the internal amplifier. The silent cd is necessary so that the cd function can be selected but only the sound from the aux device played. If you use both an audio cd and the aux in things could happen, time travel, end of the world, idk. Mazda and Ford made this process easier by opting for a modular radio design which allows easy access to the relevant circuit boards. You could do exactly the same thing with the cassette input if you don't have a cd player but you would need a way of tricking it into thinking it was playing a tape, such as one of those aux in cassette adapters, which renders this irrelevant anyway...
This will work on any car which uses the modular radio unit of the late 90s through to the mid 00s. So all mk2 and mk2.5 mx5s, rx8s and probably numerous mazda and ford boxes.

How to...
1. Remove the radio unit

Gently pry off the side trims, they are easy to remove with a prying tool, be careful not to scratch anything, tape on a screwdriver will be fine. Using suitable radio removal tools, or a small screwdriver or coat hanger wire, remove the radio unit via the holes on the sides. Disconnect the wiring loom and aerial cable form the back and remove it from the car.
*note that the cassette blanking cover is also removed in the above image, you don't need to do this.

2. Strip it down
You need to access a circuit board on the right hand side (as you look from the front) about half way down, to do this you will need to remove the cd unit, back plate, front cover, an internal cover and the side cover.


*screws are already removed in the pics
First remove the front cover around the cd slot by lifting the two top corners over the retainers, it should come off easily. Next remove the two red screws on each side, a 10mm socket may be better here, this will release the cd unit and you can gently pull it up and away from the rest of the unit.

Remove the screws from the back plate and remove it. (Forgot to get pics but self explanatory)

Remove the front cover by removing two screws from each side and prying the top and bottom over the retaining tabs.

Unscrew the plate that sits under the cd player and remove it.

Unscrew the side plate, there are a couple of screws on the front of the unit under the face plate that need to come out too. Now lift the side plate out. It's a bit fiddly as it locates into the front plate with a couple of small tabs.

3. Soldering
Now you should see a small circuit board on the side of the unit where the cd player plugs in to the main unit. Helpfully mazda have labelled what's what ????


The three left hand connections in the main block are the ones we want, labelled ch r, ch l and ground.
Take your cable, I'm my case a 1m male to male stereo cable (£1.50 from The Range), I would advise a longer cable as this won't reach the arm rest. Chop off the end that isn't going to connect to your mobile device and remove about 1" of outer sheath. Strip the ends of the three wires that are revealed and tin them with a little solder. Once tinned trim them to around 3mm. My iron was a bit hot for the thin wire and melted the sheath.
You will need to identify what each wire is, right +, left + and ground (if using old headphones you will probably have right - and left - which will need to be joined to form a common ground). I did this by opening up the connector that I had cut off, the wire to the centre of the connector goes to the tip (right +) the next one goes to the centre channel (left +) the one connected to the base is ground.

Solder the relevant wire to the relevant point on the board. You should probably reassemble and connect to the car at this point to check all is well, I couldn't be arsed so coated the connections in hot glue to both insulate the wires and help to support the joints. I also looped the wire through some holes in the cage (prior to soldering) to prevent it from pulling free if it gets caught on anything.

4. 'Reassemble Stephanie' (one for Short Circuit fans, 'Johnny 5 is alive' ;) )
Reassembly is the reverse of the above process (that should cover it!)

5. Silent CD
Make or download some silence and burn it to a blank CD as an audio file. I used two 32 min tracks from
Pop the silent cd in and it should start playing, now connect your aux device and away you go.

6. Bluetooth
I haven't tried this yet but you can get a cheap (under £10) battery or 12v Bluetooth receiver with a 3.5mm jack which you could hide away and connect to for wireless audio!

7. If I was doing this again...
- I'd get a longer cable
- I may opt for a female 3.5mm socket rather than male and install it neatly in the trim somewhere rather than having the male connector dangling in the footwell.
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