I'm trying to hook up a amp and set of subs in a friends 2002 Tahoe. I've done some searching and still have some questions. The Tahoe has a factory amplified AC Delco head (non-bose I guess, it doesn't say bose) with on star (but its not used). I think I need a special pigtail to add a set of RCAs and keep the original head unit and speaker wiring. I'm not exactly sure what its call or how it works. Could someone point me in the right direction? I pulled the head for chits and giggles and hooked up a aftermarket head with a standard harness. The head worked (powered up and tunned) but I couldn't get any sound out of the speakers, which told me that I was correct that another pigtail wiring is needed. But where do I find one?