Instructables

Adding Auxiliary Input (for an mp3 player) to an Old AM Truck Radio

Picture of Adding Auxiliary Input (for an mp3 player) to an Old AM Truck Radio
5471358543_ab422d6dbc.jpg
This is a very simple hack that will allow your older radio to play from an auxiliary input.

In my case, I am using the radio from my '66 Ford truck and using the input to listen to music from an mp3 player. The radio is about as simple as it can get: AM only, mono output but this can be done for stereo just as easily (more easily in fact!).

Here is a quick video of it in action:



The parts count is fairly low:

any RCA jack with 2 NC shunts: (sourced locally at All-Electronics but available online here for $0.50)
Hookup wire: (I had this on-hand; about 2-3 feet is plenty)
Optional 80-220 Ohm resistor (this is only necessary if your stereo is mono)
Optional enclosure to hold the jack

Tools:
Soldering iron and solder


 
Remove these adsRemove these ads by Signing Up

Step 1: Fix (Optional)

Picture of Fix (Optional)
My radio required some simple coaxing to get it working properly before I could begin hacking it. It powered on, but had a VERY bad hum that threatened to destroy any speaker connected to it.

Doing my diligent google research, I was unable to find any schematics online and only the tiniest bit of background information on my radio at all. Luckily, you do not really need schematics to do this hack (but it could make things simpler). This site is a decent resource for information on caps and radios for those that are interested.

In general, the simplest first attempt is to replace all electrolytic and paper capacitors. These capacitors almost always go bad in old radios because, over time, they dry out and their values stray. Replacing them is easy and cheap enough so this can be done very quickly.

In my radio, there are no paper capacitors and only two electrolytics. I used google docs to make an extremely crappy picture with their positions (electrolytics are polarized don't forget!) and their values. I replaced the caps, did a few other minor things, and it worked! The power cap in the picture was not replaced.

Here is a little video of it functioning:




Thanks for the great write up! I just attempted this on my AMC Eagle's am/fm stereo and am having a couple issues. For reference, I used the same panel mount jack as you.
-My radio does not cut out when the jack is plugged in, I thought this would be the case
-The aux only plays music out the right speakers, but the radio still plays everything correctly

Since mine has stereo, I assumed I could just wire pins 2 and 5 without a resistor. Don't know if this is correct or not, but both pins go directly to the source leg of the volume pot. Pins 3 and 4 are both connected to the radio input wire, and Pin 1 is connected to the ground leg of the pot. Any suggestions?
Phil B3 years ago
Image #2 in step 2 does not load. There is an error message that says, "Image not found." The notebook drawing of an electrical plug in image #6 of step 2 is labelled "RCA plug," but shows a 1/8 inch stereo plug. The attached photo shows a male and a female RCA plug. I am a little unclear if the pin numbers are printed on your radio's green circuit board, or if you assigned those numbers. This was a very popular type of project at Instructables a couple of years ago. It is less frequent now, perhaps because many cars in the last couple of years come with auxiliary jacks built into the vehicle. Thank you for sharing.
RCA plug.jpg
nonoodlez (author)  Phil B3 years ago
I went over the images in step 2 and they all seem to load fine. I wonder, is there is anybody else that can confirm whether the images are loading properly or not?

You are correct on the RCA comment. I meant mini-RCA. I'll correct it and repost in a bit.

Concerning the numbering, I did not have a datasheet on hand so those are numbers I just came up with to clarify things for myself.

Just for you to know, this was for my 66 Ford truck and this hack would be particular to this era of radios. This is really a brute force approach. If I am not mistaken, later radios (i.e. 80's and 90's) are a bit more difficult to patch into thus requiring a different approach.

Thanks for the comment!
Not to nitpick (I suppose I am though) but just a minor clarification. That's a "TRS" connector, not an RCA connector, full or mini. TRS stands for tip-ring-sleeve and can have a common slang name of "stereo jack".
nonoodlez (author)  Phil B3 years ago
Wow! I just noticed that you are quite the contributor!
When I was 27 years old there would have been no way for me to submit many Instructables. But, I turn 65 in less than two weeks. I have had a lot of time to learn about a lot of things, usually the hard way. Some of them are worth passing on. I hope somebody benefits from them. Often people who look at my stuff find ways to improve upon what I did.
OldHarley2 years ago
In order to get my AM radio working again, I replaced the electrolytic capacitors just like in nonoodlez diagram above; however, my local electronics store informed me that both the 50uf and 500uf capacitors are no longer made.

Instead, I used a 47uf and a 470uf, both rated at 35 volts and it works like a charm.

Incidentally, these capacitors have a (+) and a (-) side. Just be sure to orient the new ones like the originals. Both sides will be marked on the old and new, so it is easy to tell.

Thanks to the author for this article!