I would assume it's the connector for a CD/MD changer - is the 'box' end you refer to sealed or does it have connectors?
I have a Sony Xplod CDX-GT710. The cable is about 5-6 inches long, black, has a little 2x2 inch box at the end of it, and it plugs into the Unilink/Bus port on the back of the unit.
The only thing I could think of is that it might be some type of wireless or bluetooth adapter. I don't know a lot about car stereo's. So, someone has to know.
It's sealed. There is no place on it to connect anything to it.
Are there any additional functions when you plug it in. What does the manual say?
"In the beginners mind there are many possibilities, but in the experts mind there are few."- Shunryu Suzuki
"Do it right or don't do it at all"
[-------90%-] (New Car=New Build)
That piece fools the head unit into thinking there is a changer or other Unilink source hooked up. Once plugged in the cd changer source input is available without really having a changer hooked up. No you plug your MP3 player output into the RCA input for the changer and you have AUX input!
Ours is the age that is proud of machines that think and suspicious of men who try to.
ARCAUDIO SE Amps
Rainbow Profi CS365 & Profi Vanadium 12"
Ahhhh...that makes perfect sense. That's why I am able to plug my portable Sirius receiver into the RCA input and listen through the CD changer mode.
Sweet!!! Thanks for the help all.