So basically, I would check the wiring and all the fuses before I went out and bought anything. Then I would shorten the grounds by about 6 inches to a foot, however much you can really. You want there to be "some" slack for just in case... But the grounds should be fine, Ive learned that 3ft is acceptable. But as for making sure the grounds are good, make sure its connected to bare ass metal. Take a dremel tool to the the surface if you have to.
Now, as for the wiring kit, I would prioratize getting a new box over getting a new kit. 4g isnt all that bad. It will suffice seeing as how I doubt its the problem.
Then if its not wire, fuse, ground, or the box, I have no idea in hell.