so i bought a new kenwood ddx6019 and a metra 350z wire kit and i have a couple questions.

the ground cable from the HU it is supposed to be wired in the ground cable of the 350z harness. yes?

same with the power cable?

 

The power wire does need to be in the power wire of the nissan harness. As for the ground, as long as it is grounded it doesn't matter what it goes through. I ran all my grounds from the deck and e-brake wire (avic z2) the the screws on the outside of the white ac control box.