Ditto on the 4ga wire going forward for both power and ground. I usually use a marine 60 or 70A circuit breaker back near the switch to protect you from the energy coming forward (should there be an unfortunate impact).
One of the cars I built for a friend actually got met a tree while he was "testing" on the street... long story... but the car was destroyed and the circuit breaker tripped. While dissecting what was left, we found that part of the broken motor plate pinched the positive 4ga going forward...