Thanks to oth's help, I was able to source a replacement remote radio switch assembly. The thing I need to figure out is why my remote controls don't work at all. Most likely cause, of course, is that they're disconnected somehow. I know that before, the mute was stuck on, indicating a likely blown mute circuit. But now it doesn't work at all, making me think something was unplugged to get rid of that annoyance.

I pulled out my factory head unit and saw this:

Note that I unwrapped the electrical tape around the gray plug there just to get a better look.

Another shot:

And a close up, linked for its size:
http://imgur.com/UROtj.jpg

Anything unusual looking?

If I understand http://users.rcn.com/dhintz/Michelle/Audio/audio.html correctly, then:
- single yellow/green loose wire is the antenna relay
- green/red wire is dash remote
- yellow/blue wire is mute
Is that correct?

Alarmingly, I can see exposed nicks on both green/red and yellow/blue wires. When I was looking at the wires in person, I thought at least the two exposed parts wouldn't touch each other. I'll be covering them with electrical tape.

Here's the current state of my system:
- radio stations work
- head unit works just fine
- remote controls don't work
- mute light doesn't come on or off when I press mute

It doesn't look like anything is majoring wrong with wiring harness behind the head unit -- no melting or scorch marks. I don't see any seriously weird hack job, outside of the nicks. So assuming (big if ) the wiring harness is good back there, am I right in assuming that the next likely cause of a non-op remote control is because the remote control assembly has been disconnected from the plug behind the dash bezel?

Anything else I could try to diagnose? I wonder if the nicks were from someone trying to test the signals while the radio was on and playing. What other things should I look through to see where the disconnect might be?

My next step is to get the dash bezel off and have a look. The reason I'm dragging my feet is because it's a much more eye catching part of the car and I don't want to scratch anything.