Hope this will clear some things up.

The factory head unit does not have an amplifier in it. All it has is rca pre-outs. At the factory instead of using rca cables, which most people are familiar with, they wired it straight to the preamp using the wiring harness behind the stereo. People have been connecting the amplified leads from after market stereos to the stock rca wires going to the amp. I would not suggest this. While it may work for some time there are severe problems with this. One the amplified signal from the after market head unit is very dirty. Audio signals that have gone through a gain stage take on massive distortions. Second the signal has far too gain to properly integrate to the stock amplifiers.



What should be done is that the stock left and right channel leads should be cut from the wiring harness and terminated with rca plugs. Then these can be safely plugged into the pre outs on an after market head unit.

I hope i explained this well enough for you to understand. If not let me know and I will try to explain it better.