After further investigation, I have found that the existing negative wire is about an 8 gauge wire. So it is bigger than I had thought. Now my question is whether I should try and wire the ground of the amp directly to the negative battery terminal? I have 2 spots in the car that are getting grounded, the amp and the head units. I think that this is causing some issues, and if I can get rid of the amp ground spot it won't be a problem anymore.