New headunit instructions

Ive looked all over the internet but they're so hard to find for our cars. Anyone know where I can get good instructions on how to install a Kenwood double din headunit?

Ive also heard a few people talking about it being a really hard process because you have to run wires to bypass the factory amp of something like that. Do I really have to do that, or can I just plug/splice the wires from my stock headunit into my new one?