Help with wiring head unit
 

I am in the process of putting in some new audio equipment in my car and was wondering what the brown harness goes to. In all the DIY write ups I have seen, there is nothing plugged in in this location. This is a non bose from a 2006. Here is a pic from one of the DIY's that shows the location I am referring to.

My wiring harness came in today and there is indeed only 2 harnesses. Anyone know what this is for? I have 3 harnesses plugged into the back of the stock radio and only 2 come with the wiring kit.

Can you explain more? Like what youre installing, etc.

Installing HU, amp, subs, and components. I have wired a few systems in the past and have no problem with everything else. I am 99.9% sure that this is the harness for the stearing wheel audio controls, didn't think of it at first because I have a base and have no audio controls.