2006 acura rsx type-s w/bose amp woofer

Hey everyone I am going to purchase a sub and amp to install in my 2006 acura rsx type s with the factory bose system. I would like to tap into the speaker wires at the factory bose sub in the trunk. How do i know which one is the + and - speaker wires as there is no way to do the polarity test using a battery on this speaker. I could also    just tap into the factory harness behind the radio and using the line output converter get a good signal. I would prob have to use the output converter no matter where i get signal from as this is a factory amplified system. Thanx in advance fro your help and i am hoping someone can answer these questions. thanx again

It really won't matter. If you're not removing the factory sub, at least disconnect it. You can always switch polarity at your new amp or sub. Play it both ways and see which sounds more accurate and gives you better response.My ex once told me I have a perfect face for radio.