It is fairly easy to add subs to your stock system. To start you need to find out if your amplifier (see below for determining what amp to use) will accept speaker level inputs. Speaker level inputs are a signal that is strong enough to drive a speaker without an amplifier (Basically a pre-amplified signal). If you don’t know if your amp is capable of this, just ask your stereo sales guy or check your owner’s manual. If your amplifier will not accept speaker level inputs, they you will need to buy a converter that will change speaker level inputs into line level inputs. Line level inputs are a signal that is not strong enough to drive a speaker, hence needing an amplifier. Once that is determined, everything else is the same. You will need to run power wire and a fuse from your battery to your new amplifier (see below for determining what size wire you need). I would recommend at this time that you spend the money and get a proper positive battery connection that accepts additional wires out. Put the fuse within 18” of your battery. The fuse on the main line is not to protect the amp, but to protect the wiring. Connect the power wire to the amp as per the specs. Now take a short piece of wire and connect it to a solid metal piece on your chassis. Connect this piece to the negative power wire input on your amp. Run the wiring down the left side of the car, as it is the easiest to do. Once your power wire is run, you will need signal. The easiest place to get signal on a stock stereo car is the rear speakers. Here you will need to splice one of the rear speaker leads so that you will have signal to the rear speaker and to your amp. Here is where your amp choice becomes an issue. If your amp accepts speaker level inputs, then you just connect the feed from the rear speakers directly to the amp as per the manufacturers specs. If your amp does not accept speaker level inputs, then you need to put your feed from the rear speakers into the line level converter, and then from the line level converter to your amp. Congratulations your amp now has power and signal. The only thing left is connecting the speakers. For the purpose of this discussion I will assume that you have your subs already mounted in a box. Mount your amp somewhere where it will get airflow and not be bumped around. Connect your sub speaker leads to your amplifier per the manufacturers specs and viola, you now have sub bass!
or is it just a stupid idea 
classic noob mistake 
I was just making fun of myself since I thought I had washed all the "noob" off. Hmmmmm, must have missed a spot 
