Resources for building wire harness

Hi All

A little background to my request. I recently inherited a fairly untouched 56 ford F100. Sometime in the mid 80's this pickup had an electrical fire in the headlight circuit. The wiring was hacked back together and then never properly fixed. Fast forward to today, the headlights are no longer working.

I would like to keep this pickup as original as possible and cant seem to locate an OE replacement wire harness. I am fairly confident I can source all the needed connectors, but am curious what resources may exist to get wire gauge, color, length details. He existing harness is poor enough shape that I don't think it will make a good template.