In my 2016 FB22 Sport which was purchased new, the radio has always given me fits. It wasn't long into our first year of ownership where it just gave up the ghost and quit. It all started with the main plugin to the back of the radio. On the unit itself, it developed an eternal short. Some days it would work, others it would not. Like the day I took it to the dealer to be serviced. It worked that day. But, the day I brought it back home...it refused.
So, what to do?
I replaced it with a big and better version. It was a single DIN but had a roll out screen. And, it had "BlueTooth" which the OEM radio did not. Sadly, like it's predecessor it only lasts a couple of years.
Tired of fighting this issue and having found ways around the unit being a necessity. I again bought a new unit but returned to the cheaper options.
I installed it, and I could see it was working. BUT, there was "zero sound". Nothing!
I started to trace the circuitry and racked my 78-year-old brain for all the reasons it wouldn't play. So, as a workaround, I connected a set of speakers directly to the radio. It played!
Next, I checked the continuity of the trailer's wiring from the radio to the speakers. It was good. But, and this is a big "but". I didn't disconnect the wires from the speaker connections.
After trying all sorts of tests I finally, pulled off the speaker connections and connected a direct wire from the radio to the speakers. Walla! Sound poured out of the speaker loud and clear. So, I reconnected the speakers to the trailer's wiring and it WORKED!
After close observation I noted that the speakers are nested in a "hole" that has been created in the insulation between the inner and outer shell. Over the years the connections had built up oxidation much liker a corroded battery terminal. I took the speakers down and with a fine file, I cleaned the speaker posts. I also cleaned the wire connections. I reconnected everything and I now have sound.
Therefore, if your radio decides to give up the ghost for no apparent reason. Before you rip it out. Pull out one of the speakers and look at the connections.
Final note. This perplexing issue appeared as I was "de-winterizing" the trailer after a Montana winter that I thought would "never end"!