OleStraightStick

So I’m ditching the factory speakers and running RCA’s to a 5 channel amp, but wouldn’t mind some details on how to tap into the power/accessory, back-up cam, etc.. In my thread in c5gen, it was mentioned that I need a basic gm harness, which I’ve read on another website too.. does anybody have any links or a part number? Maybe a link to a detailed thread or advice on how y’all wired in your head unit when running all new speaker wires (since I can’t use the PAC harness).. thanks a bunch, y’all.. got the interior torn apart and need to order this harness soon..