What is third connector on factory radio 05 Tacoma?

Just upgraded my factory radio to a Kenwood. Original radio (non-JBL) has 3 connectors (not including antenna). One connector is power & front speakers. Second connector is rear speakers, but I don't know what the third connector is! Almost same size as power/front speaker connector.

Anyone shed some light on this?

Thanks

Terry

 

?

 

http://www.customtacos.com/tech.old...06toyrm/06toypdf/06rmsrc/rm2006ta/0550016.pdf

Audio/Visual
Audio And Visual System: Parts Location
Audio And Visual System: System Diagram, System Description
Audio And Visual System: How To Proceed With Troubleshooting
Audio And Visual System: Identification Of Noise Source
Audio And Visual System: Problem Symptoms Table, Terminals Of ECU
Audio And Visual System: DTC Check / Clear
Audio And Visual System: Noise Occurs, Sound Quality Is Bad In All Modes
Audio And Visual System: Sound Quality Is Bad Only When CD Is Played (Volume Is Too Low), CD Cannot Be Ejected
Audio And Visual System: CD Cannot Be Inserted Or Is Ejected Right After Insertion
Audio And Visual System: CD Sound Skips
Audio And Visual System: Radio Broadcast Cannot Be Received (Bad Reception)
Audio And Visual System: Steering Pad Switch Circuit
Audio And Visual System: Illumination Circuit
Audio And Visual System: Speaker Circuit
Audio And Visual System: AMP Mute Signal Circuit (From Radio Receiver Assembly)
Audio And Visual System: AMP Sound Signal Circuit
Audio And Visual System: Sound Signal Circuit Between Radio Receiver And Stereo Component Amplifier
Audio And Visual System: AVC-LAN Circuit
Audio And Visual System: Radio Receiver Power Source Circuit
Audio And Visual System: Stereo Component Amplifier Power Source Circuit
Radio Receiver: Components, Removal, Installation
Radio Setting Condenser (For 1GR-FE): Components, Removal, Installation
Radio Setting Condenser (For 2TR-FE): Components, Removal, Installation
Front No. 1 Speaker (For Regular Cab): Components, Removal
Front No. 1 Speaker (For Regular Cab): Installation
Front No. 1 Speaker (Except Regular Cab): Components
Front No. 1 Speaker (Except Regular Cab): Removal, Installation
Front No. 2 Speaker: Components
Front No. 2 Speaker: Removal, Installation
Rear Speaker (For Double Cab): Components, Removal
Rear Speaker (For Double Cab): Installation
Rear Speaker (For Access Cab): Components, Removal, Installation
No. 1 Speaker With Box: Components, Removal, Installation
Radio Antenna Cord: Components, Removal
Radio Antenna Cord: Installation
Radio Antenna Holder: Components, Removal
Radio Antenna Holder: Installation
Radio Antenna Pole: Components, Removal, Installation
Voltage Inverter: Components, Removal
Voltage Inverter: Inspection, Installation
Steering Pad Switch: Components, Removal
Steering Pad Switch: Installation

 

Thanks! I've got my homework cut out for me.

 

If there are 3 wires on that plug then it's the steering wheel control.

 

Yes it does have 3 wires, but I have no steering wheel control(s). It's definitely R3 that I'm questioning. (Steering wheel control). Guess its connected even if the vehicle does not have a steering wheel controller.

Thanks all!

TB