2008 JBL Factory Wiring Help

I have spent hours searching but cannot find anywhere talking about this 3rd plug on the back of my 51856 JBL Non-Nav 6CD Changer (86120-0C260 or CQ-ET1760X) for my 2008 Sequoia Ltd. All the stereo upgrade guides, including Crutchfield and my PAC RP4.1.TY11 kit instructions cover the top 2 plugs but do not include this 3rd plug and do not talk about it. Is this SATELITE RADIO? BACKUP CAMERA?

 

Here’s a thread that helped me:

https://www.tundras.com/threads/ultimate-wiring-diagrams-collection.81448/

incredible work, has all of the electrical information you could want for your vehicle.