I don't have much mechanical experience, but I have a lot of experience tinkering with electronics... so here is my contribution to the board

I just modded my Becker Europa stereo to add an aux input. It took me about 1 hr including figuring out what the hell I was doing and how I was going to do it. These steps are what I did with that radio, but my guess is that the same could be done with many old radios.

I did this
a) because I am cheap and didn't want to buy another radio
b) because I like the look of the becker in the car and thought a modern stereo would look weird in a 30 year old car.

Tools/materials: soldering iron, insulated wire, 1/8" female jack, drill, 12v DC wallwart, speaker.

So here are the steps:

1) I took the radio out of the car, brought it inside. Hooked it up to a 12V DC power supply and a speaker.

2) Took off the top and bottom lids of the stereo - they just pry right off - held in place by friction.

Most (about 3/4) of the insides of the radio is for the AM and FM tuner part of the radio. There is a separate circuit board for the amplifier circuit, which is what you want to find. It is easy to find because it is located directly behind the volume knob, extending from the knob to the back of the unit.

Make sure you have the radio oriented so that the solder side of the amplifier circuit board (as opposed to the component side) is facing up towards you.

3) Now we will take a little aside and you need to make a simple audio probe:
a) Take an old pair of headphones - how about those crappy ones you got for free on the airplane that time? Cut off the headphones so that you have just the jack and the wire coming from it. Strip the wires back to find the left and right wires (usually insulated) and the ground (usually just bare wires wrapping around everything else...

b)Attach the ground to the ground lug on the back of the stereo or in some way make sure it is making constant contact with the metal chassis of the radio (aligator clip?), and twist the left and right wires together to form one wire.

c)plug the jack into anything with a headphone jack and turn the device on with the headphone volume turned up half way.

There, you have an audio probe.

4) With something playing on your audio device, take the audio probe and hunt around on the amplifier circuit board poking it on solder traces on the board until you hear audio from your device coming through the speaker.

Hint: Look near the back of the amplifier circuit board, you will see a few wires coming off of the tuner board and connecting to the amplifier board.

Another hint: if you see a little spark when you probe a trace, avoid that spot - you won't blow anything if you just hunt quickly, but don't dwell on spots that don't work.

5) When you find a spot where the audio comes through, test to see if the volume knob works to turn your sound up and down, also check the tone knob. If both work, make note of that spot. If the volume knob does nothing, or if you hear audio but it sounds colored or unclear, move on, you will find a better spot.

6) Solder a wire to the good spot you found on the circuit board.

7) run the wire to a 1/8" female jack and solder it to the tip connection of that jack. If you use a stereo jack, wire it to both tip and ring spots (the europa is a mono radio... so I guess calling it a stereo all along was a misnomer )

8) solder the sleeve connection of the jack to the ground on the stereo - you could use the chasis or run a wire to the lug on the back, or if you are really daring, look for the ground on the circuit board and solder to that.

9) If you haven't already, you'll need to take the faceplate off, but I think you had to do that to get the radio out of the car. Drill a hole in the faceplate in a spot where the jack won't be in the way when you put it all back together. The hole should obviously be big enough for the 1/8" jack.

10) Mount the jack in the hole.

11) put it all back together! and put it in your car! Use a 1/8" to 1/8" male to male cord to plug your audio device into your stereo.

The best way to do this would be to have a switching jack that disconnects the connection from your tuner to the amplifier when you have something plugged in the jack. However, what I have found is that when you have audio going to the radio from an external device, it totally drowns out the radio and I do not hear anything at all from the radio - even between songs, and even on the best tuned in FM stations. I think it is because the output from the headphone jack on an ipod or other device is so much stronger of a signal than the un-amplified signal from the tuner board.

For me, the radio automatically returns when I unplug from my MP3 player.

You could also set it to an AM frequency between stations, where there is very little background noise...

Also note this is for the Europa, which is mono (even though the signal is split to two or more speakers). If you were modding a stereo radio, you would need to find the left and right channels and wire separate wires from those traces to the jack. A little more work, but still not that complicated - just hook up a speaker to each channel and probe around and take note of which traces go to which side.

I know this is a ghetto way to do it, but for me it has worked to total satisfaction - way better than an FM transmitter. When I have something plugged in to my aux jack, it works flawlessly, I completely forget it is a 30 year old radio

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