Stock wire gauge alt to battery

[4X4XFD]

2002 FX4 4.0L, auto trans. What is the stock wire gauge size between the battery and alternator and grounds? I've upgraded to a 160 amp alternator and need to determine what gauge additional wire (in parallel with stock) wires I need to add to handle the higher output alt. I'm guessing the stock wiring is no larger than 8 awg. I'm not going to tear into the existing wiring looms to replace what is already there. Adding additional wires with what is already there should serve the same purpose and be a lot easier.
Assuming stock wire gauge is 8, I'm thinking adding additional 4 awg wires should work.

 

[SenorNoob]

According to calculator, a single 4 would be sufficient to car 160 amps. One 8 gauge and one 4 gauge gives you an effective 3 gauge. So would be fine.