do you know what what wires you used? I assume the front woofers?
Also wouldn't it be easier to use the stock amp's ground an power????

 

I used the right rear speaker. Look at the diagram above. I used pin 9 (black) and 24 (green) from connector P32. in my old car I used the left rear because it was the easiest to get to.
To avoid any alternator whining noise I went straight to the battery also because for me it is located in the trunk. Easy access....

 

My battery is in the engine bay, so a little inconvenience.

 

Not really. In my VW I ran the positive cable straight through a grommet in the firewall, and the ground I just used a chassis bolt in the trunk area where the sub was...

 

I have a NX200t so had to run the power wire front to back, if you do decide to do this, remove the windshield cowl, trust me it'll change your life.

The problem is the best factory grommet to use for the NX is in a ridiculous spot (unless you drill a hole which I didn't want to do), on my former Camry and Corolla they were in much easier spots to access.