Originally Posted by projectRDM

That is NOT the way to do it. For starters you don't use different gauges of wire for positive and negative leads, they should be the same. Consider the voltage like a water hose, the in and out need to be the same size.

Secondly, the ground should be bolted to the chassis by the battery. Running it back to the engine bay creates a shit load of extra resistance that's not required. The engine will be grounded to the chassis already and you're not going to see a ground loop as long as both grounds are good and clean.