Before we go any further, Let me post a little disclaimer. I am certainly NOT an electrical engineer. I don't even play one on TV. And, I didn't stay at a Holiday Inn Express last night. Also, I am not the originator of this idea, but I gathered information from several different sources and combined them into one easy to follow guide, so the next person that tries it doesn't have to do all the 'trial and error' work that I did. Hopefully, You'll find the directions easy to follow. Remember, there is always a chance that this could screw something up- Either your radio, or your MP3 player... So far, I have had no problems, although mine has not left the test bench yet. Just don't say I didn't warn you!
First things first. Your sound output quality will only be as good as the weakest part of the system- Which is almost certainly the old factory radio. Do yourself a favor, and 'tune it up' a bit using the simple fix I posted here- http://www.slick60s.com/viewtopic.php?f=5&t=25847. It fixes a lot of buzzing/static issues, and will greatly improve the end result!
The parts list is short- And you can get it all at your local radio shack....
- -1/8" Stereo Jack, Radio Shack P/N: 274-246
-100 ohm resistor, Radio Shack P/N: 271-1108
-Wire, 22 or 20 ga
-Soldering Iron
-Solder
That's all you'll need. Should be less than $5 for all the parts.
The conversion is easy. First, You've got to do a bit of work to the plug connector. If you get the same one that I used from Radio Shack, You can follow this photo/diagram exactly-
If you use a different connector, you'll just have to figure out what goes where. Pins 2 and 4 on mine were the left and right channel, and we're combining them, through the resistor. Pin 1 is the common, or ground. The other two pins have no use in our application.
Just solder the resistor between pins 2 and 4. Then attach one wire (I used GREEN, but you can use whatever you like) to the resistor. This essentially connects the green wire to both 2 and 4, through the resistor.
Then, solder the black wire to pin #1. This is the common wire.
Now, it's time to make the connections inside the radio case. You are going to need to solder the two wires that are connected to the stereo jack into the radio. The connections are going to be made on the small circuit board that's connected to the volume/tone adjustment knob, at the same spot that the sound input from the radio tuner is. Here is a photo of where they go-
Just run the wires into the case (I used the hole that the speaker wires exit), then connect them to the board as shown. Couldn't be easier.
Now- Power the radio up, step back, and enjoy your handywork-
Now, You and your slick have entered the 21st century.
I use an Iphone, so I can route all my calls and other audio right through the radio as well. Now, If I can just get that truck back on the road, I'll be all set!
-Andrew
Note- I updated this thread on 1/7/2017 to replace the missing photos. Hopefully someone is still getting some use out of it!