I have checked around but am still not sure on the factory harness wiring. I have a 2010 STD Cab Silverado nonbose system (so there is no factory amplifier) Here is what I have come up with...

On one harness there is...

Green = <-------- ??not sure why two??
Green = RF Speaker +
Light Green = RF Speaker -
Light Orange = LF Speaker -
Grey = LF Speaker +
Yellow = Illumination yellow (dimmer) + <-------- ??not sure??
White/Red = 12v +
Black = Ground -

On the other there is...

Brown = LR Speaker -
Yellow = LR Speaker +
Light Blue = RR Speaker +
Dark Blue = RR Speaker -

Harness pics at http://trueambition.net/138stuff/resize.jpg

Any help would be great! I am trying to install a MTX Req 5.