hi jason,
i've been wanting to install an aftermarket headunit really soon, and was told that the easiest way to install it would be to buy a wiring harness from super cheap auto (cost around $15-20).
from what i was informed, they are make/model specific, and plug straight in, so you only have to connect up the wires to your HU, and no messing about trying to figure out what wire is what, as it is all labelled. the pro of this is that if you ever want to put the stock unit back in, it will just plug straight in.
disclaimer: this is what i have been told, i have not actually gone out and tried to buy a harness, nor have i installed a HU before, still in the process of sourcing it.
hope i helped =) if its wrong, disregard