I have an existing 110 outlet that I tapped into to create a new outlet on the other side of the wall. As seen in the photo, the existing outlet is in a "series" (two hot and two neutral coming and going). I ran new wire for the new outlet, inserted the leads into the back of the existing plug. All blacks test hot and whites don't. I hooked up the new outlet, tested it with a plug tester and it is telling me that the hot and ground are reversed. This doesn't make sense to me since all blacks test hot and and white and ground do not. In the picture the wire with the yellow sheathing is the new wire run to the new outlet. Can anyone shed light on this? Thanks!