I was doing some work to this truck for a friend, the radio was working fine the previous night but I turned to down to see if I had fixed an exhaust leak.  The next day I pull it out front to figure out the non-op fog lights.  I pull the fuse panel and find the Edge CTS monitor stuffed behind the cover.  I know it was smogged earlier and was unplugged.  I proceed to reload the tune, always been set on economy, not that it helps with a 6.0 gasser.  As I'm going through the motions, the tuner asks me to pull the radio fuse.  I pull a fuse from the PDC labeled RAD and continue loading the tune without issue.  My friend comes to get the truck and the radio is on but no sound.  Tried to reset the radio(Kenwood DDX24BT) but no dice, same issue.  Tried adjusting source levels, volume levels, every option on the unit and no sound.  Upon further inspection I find a fuse in the inside fuse box labeled RDO.  I'm thinking maybe that's the fuse I should have pulled.  Did I possibly hurt the radio?  Google isn't helping much.  I plan on trying to reload the stock tune and remove the Edge to see if that helps.  My friend took the truck home so I will have to swing by her place later this week to try it. 

Most stereos have two power sources. Yellow is typically a constant 12V connection for memory and clock. Then the Red lead is keyed hot which triggers on the stereo.

I got the stereo making sound again, not the way I had thought though.  Playing with the tuner got me nowhere so I pulled the stereo out to see if something had unplugged.  I've never seen a stereo wired the way this one was.  The speaker wires coming from the head unit were taped off and not connected to anything.  The speaker wires coming from the harness were looped around and went right back into the dash some where.  Her son used to have a fancy stereo setup i this truck so I imagine it was because of equipment it used to have.  I cut the speaker wires on the harness and hooked them back up to the wires on the head unit and it worked.  All I can figure is that whatever doohickey the music was coming from before failed at an odd time.