Chris, Just copy what the factory did.
They had a team of engineers and techs figure it out; wire size, how to route, how much strain relief, etc etc (or yada yada yada for you new yoorkers)
i am following the factory wiring diagram. I bought an nos full chassis harness , had an electrician come out and check the thing for continuity. It’s good. Yet I have no power passed the starter relay. So I’ve finally got a new starter relay in after waiting MONTHS. Hopefully that solves it.