The factory wiring is bigger than 4ga. I know this because I bought some 4ga connectors with the thought of extending the stock wiring and they would not fit. Also I eventually ended up using a 4ga replacement wire from the Neg. terminal to the ground point on the body and that wire is thinner then the stock wire. That's why I was concerned that the replacement wire might not be thick enough, because it doesn't match the stock wire.