On my class A the dash radio is a Pioneer.. Now out of the box it does not have this feature. In my first towed. The replacement dash radio (the original died of old age) was a Kenwood. it too did not have this feature out of the box.
On both of them I plugged a box into the port on the backside and instant LINE IN. (AUX in) note there are several plug ins like a multi cd changer and XM-Radio but I plugged in an AUX in.
Play Cassette tape. CD or MP3's or portable radio (Though why you'd do that I don;t know) through the system.
Note that most modern Dash radios have one of the following options.
Blue tooth (Connect your Streaming device direct to the dash radio/system(
Aux in (native)
Aux iu (Add on like mine)
NOTE also when using AUX in I have to either use an inverter and wall wart to keep Phone charged or let it run on battery Using a 12 volt type charger will cause all sorts of **** on the audio feed (Ground loop issues)
IN my current car (Factory original radio/Cassette) I use a cassette adapter This looks like a tape but with a cord coming out that plugs into the streaming device.
Works great. I get the full power of the dash radio system while I listen to say Kingston Trio performing the Ballad of the Shape of Things Caution. the first time you listen to that track DO NOT BE DRIVING.
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times