Re-wire questions
 

I want to re-wire my whole car as the last owner made a complete mess of it.
I ordered new speaker wire etc, later to find out that my car has a stock harness, and i've seen that some people 'tap' into it or buy the harness. Since i don't really want to spend more money to do this, could i just bypass the harness and run speaker wire from my speakers to the head-unit's connections?

Also, my stereo still works when my car is off (like literally off, no key in ignition). Where do i plug the remote wire in so that it will only work with the key? i'm scared this will kill my battery if i forget to turn off the radio.

What year, make and model of vehicle is this?