they tap into your speaker outputs of your amp, or if you dont have the ba system they would tap into the speaker leads out of your radio. they look like this
ill do $10 shipped and if you want 4 channels you will need 2 of them if so ill do $15 shipped.
what type so stock system do you have? BA or non BA?
and how is your amp wired right now? where are the rca's coming from?