I have a 2005 F350 Lariat dually with 55k miles. Today, for no apparent reason, the radio stopped transmitting sound to the speakers. I had all radio function, but there was no noise. The windows, cruise control and all other elements work fine. I have had no other problems. Is this a fuse, relay or what? I tested what I thought to be the fuse, and it seemed fine. Only thing is I hadn't driven it in a while, but the radio worked when I first got in. The problem occurred after I had driven ~20 miles.
Run the radio self test. Hold down the 2 and 6 button at the same time it will pop up a dtc and a failure list. The radio must be on for this to work and the buttons 1 through 6 each one once in self test gets you into a sub program. So report back