Drop in a harness DWG. The page finds the latest revision (the one without the X), traces every wire along the branch lines from table to destination, and totals the wire by gauge and base color with part numbers.
Wires that don't run on the drawn branches, plus any length added inside the panel. Enter inches from a real MDP and the BOM updates. Change them any time the MDP layout changes.
Rules: dashed (loomed) and solid branch lines are both counted. Splice circuits count the run to the splice plus every leg. Striped wire is totaled by base color. Plugs, pins, lugs, butts and loom are left off. Bus bars and other callouts above a table are listed when they carry a part number.