You don't need to run a power wire all the way from the alternator to the battery. Simple way to do it is get a 4 pole on/off switch. Run the positive just as you have. There are 3 wires on your alternator look for the green one this is the voltage regulator splice that wire and connect two long wires to run back to your on/off switch using the smaller poles on that switch hook one of the wire up to each. The green wires send signal to the alternator to charge when the power is cut via the switch in back the alternator stops charging so when you turn of the switch you are cutting both the battery and alternator power to the car and it kills. No need to run a live 4g wire all the way to the back of your car.