HoosierContour, 4AWG is to small. It will work initially, but you can burn it out rather quickly. Minimum 2AWG runs with very good grounds. Even with this size I'd run both + and - front to back, plus ground the - at each end to keep from getting to large of a voltage drop. If you run a high powered stereo, run a 0AWG with good grounds on each end.
One way to check your grounds is to watch your battery cables for corrosion. If they corrode very quickly, say within a few weeks to a month, improve your grounds and/or increase the size of your wire. Used to see this all of the time when I worked at a stereo shop installing custom systems.
