I just bought a 2003 Monte, and was wanting to add an amp and subs that I already own, but I can't seem to find a diagram of the wires going to the amp in the trunk. Am I going to have to invest in a special harness? Or is there somewhere I cna get a diagram for those?

 

what i did for my 01 was get a converter for the rca's and ran the pwr to thru the car to the the battery and then found a ground for the negative.

 

Your only real options for adding subs/amp to the stock head unit and amp setup is to use a line out converter. The problem with this, is that you will have to splice it into your back speakers, and any fading you do from front to back on the head unit will also affect the subs.

But you can find loc's all over on eBay, or just go to your local car audio store.

 

I installed my subs and amp into my 04 ss last week and I used the LOC wired to the wires coming into the factory amp (left and right rear speaker signal coming from head unit) with the amp remote wire wrapped around my cluster fuse.