The left rear speaker is the speaker that uses a brown positive wire and negative yellow wire.Here is a wiring diagram for the original factory stereo hookup info.
Radio Constant 12V+ Wire: Orange
Radio Switched 12V+ Wire: (Class 2 Serial Data)
Radio Ground Wire: Black/White
Radio Illumination Dimmer Wire: N/A
Radio Antenna Trigger Wire: Dark Green
Radio Amplifier Trigger Wire: Pink
Front Speakers Size: N/A
Front Speakers Location: N/A
Left Front Speaker Wire (+): Tan
Left Front Speaker Wire (-): Gray
Right Front Speaker Wire (+): Light Green
Right Front Speaker Wire (-): Dark Green
Rear Speakers Size: N/A
Rear Speakers Location: N/A
Left Rear Speaker Wire (+): Brown
Left Rear Speaker Wire (-): Yellow
Right Rear Speaker Wire (+): Dark Blue
Right Rear Speaker Wire (-): Light Blue
Hope that helps and best of luck.
