That is not extra wire, that is the entire brain unit with harnesses, and data cord. If your brother did that, thank him for being the coolest brother on the planet for getting that stuff for you and trying to install it.
And without insult take that to a professional and have him install it correctly. I have been installing and selling for 10 years, and that install is going to end up being a long list of issues in the future.
taking it to a shop will cost you about $150.00, but trust me, in the long run it is good money spent.