I set the old harness on the floor and made a new harness next to it, I would solder a wire (soldered uninsulated terminals/shrink wrap first) to the new harness & cut that wires' counterpart out of the old harness so the new harness took shape and the old one dissappeared so I had an exact duplicate. I bought alot of wire as you definitely want to keep the same OE colors & some have tracer colors but there is a company (maybe more than one) that sells any length of any color wire you need. I went larger on most of the wires (1 ga number smaller) and added some circuits & used new brass terminals from NAPA 725145 female and 725147 male (pricey tho, 99 cents ea) & scrubbed/reused the plastic/bakelite connectors. I can say it was ALOT of work, not sure I'd wanna do it again but my voltage drops are miniscule now