2004 Chevy with Bose System

If you're simply adding a sub amp, then just take a look at the harness at the back speakers, and simply "pop" for polarity.  Then use LOC's to step down the signal, and you're all set.

If you're adding an amp to the factory system with the factory deck, here's what you do:  Locate the factory amp.  Now disconnect the harnesses and check for continuity between pairs of leads to find your different speakers- again, popping the speakers for proper polarity.  Now that you know what's what,  wire in your LOC's and you're all set.  If you're feeling lazy, rather than running new wire to all your speakers, simply run your amp's outputs up to the factory amp's outputs and tag on there.  If you do this, you'll obviously have to cut the wires coming out of the factory amp- with one side going to your new amp's inputs (LOCs) and the other side going to your new amp's outputs.

I hope this is what you needed.  If not let us know, and I'm sure someone here can get an answer for you.