I used a wire tap, the ones you get from autozone, walmart, any electronics or automotive store really. 4 years never had a problem.
You gotta punch out one side in a sense because out of those 2 tunnels, only one of them runs all the way through. The other is like a half tunnel but has a thin wall stopping it from being a full tunnel. Just use a small punch or straight pick to remove it, insert both wires by stretching the wire tap open like a big jaw, and crimping it on both wires. Voila! done.
I dont think they have black, but I just spray painted it black so it wouldn't show. Blends in well. Mine was originally blue, looked bad lol.