The wiring harness from the Magnum does not have ACC, so it appears I have to run an ACC line from the harness/AVIC to the car. But, according to my wiring diagrams, the ACC is a negative polarity from my wiring harness. If I tap this line and connect to the ACC on the AVIC, will this screw it up? It's a negative polarity to positive, correct? Help, I'm having brain fart!

just tap it off the cig. lighter. it is an ignition switched 12v+ source.