By the way, there is a new addition to the Cassette replacement cable method. I think someone else on the site mentioned it. Sorry, Not sure who.
You have to get a Double Pole, Double Throw switch. On one switch, you have the wires that power the radio, just like my original design. On the other switch, on the OPPOSITE contacts, you connect the ground wire from the AUX, and a feed to the ground lug of the 8 pin DIN connector. This eliminates the loading effect that the MP3 device has to the radio audio level. There is still a minor amount of MP3 noise bleed from the effect of the stereo differential, but almost negligible. Ideally what we need is a 5 pole, double throw switch.
One pole for radio on/off
Opposite side throw for..
One pole for Aux ground
One pole for Aux Left
One pole for Aux Right
I made a cable for Paul. See attached picture.
If anyone else is interested, drop me a line and I'll make some up. At the moment, I don't have any spare connectors. I'll have to go to the wholesaler and get a new supply. The 8 pin DIN connectors are not easy to find. I'll have to see if I can find a 5 pole switch, though that would likely be an expensive switch.