Toyota A11713 radio and cables
 

So I pulled out my old radio and behind it theres the power cable and antenna but theres also one more cable that is plugged in alongside the antenna port and tracing it as far as I could it seems to runs along with the antenna cable as well. It runs down to where my shifter is and I would like to know what it is. I have a 1997 camry LE, 4 speakers 2 tweeters and a 6 speaker amplifier. The cable I hold it not the antenna cable but was plugged in next to it on the right side of the radio in the smaller port.

https://goo.gl/photos/6kf6YU5Prxz2ZuxL8

The round plug is for a CD player that can be installed below the radio.