[Jason Novak]

If it's showing an ERR on the CD player then it does sound like a wiring issue with something other than the audio wiring being tapped into. Is this that stock radio that came with the car, do you have a picture of the front and does it have a date on it? The circuit board is a bit different than I recall, the placement of the connector and the chip in the middle.

Compare to my 98:
http://www.ls1tech.com/forums/6865143-post5.html

Or to this 2000:
http://www.ls1tech.com/forums/7692161-post45.html

There should only be one wire coming from the CD module, so it should be easy to track down, and although the wire colors seem to change over the years the audio signal positions have stayed the same, and yours look right based on that (the one on the right).

Here's how to probe the connector for the audio pins:

"I had a stereo connector and hooked into a 12v power supply, you may need to run it off the car's connector. I made a probe by cutting off the end from an old set of headphones, and hooking the left/right channels together, and the left/right grounds together, and then each to a paper clip, plugged it into a female/female adapter, and then into a set of speakers. You could also just cut off the end of some headphones and probe using the headphone ends, just be careful because you can get some really loud tones. Put the ground probe onto the metal case of the stereo, and then tap each pin looking for sound"