I am in the process of re -wiring 2two OC-3 . I am going to follow the wires and replace each as I go .one OC-3 has a 12 volt battery and the other has a 6 volt battery. 2 questions ;can I use the same gauge wire for both and what would be the best gauge wire size to use
The gauge of wire you select is determined by what your load current is at the device. You usually do not want to load a wire more than 80% of it's rated ampacity. For instance: a 35 watt headlight @12 volts is going to draw about 3 amps. A 35 watt headlight @6 volts is going to draw about 6 amps. A # 16 AWG wire routed in a conduit or hot engine bay is good for about 8 amps. So in this example you could use #16 for both voltages. Each device will be different. Charging circuits from the gen/alt to the battery are generally 30 amp or # 10 wire.