Year one sources all harnesses from vendors - they aren't in the manufacturing business. M&H does most of the Year One harnesses and all the Mopar AFAIK. Their online catalog is excerpted from Year One catalog pages.
Evans is a Mopar only wiring vendor, but doesn't do dash harnesses.
As dash harnesses go, the firewall bulkhead and fuse panel are a lot of what you are paying for and they are the weakest pieces. Unless you are trying to do a full factory restoration for showroom stock judging, reproduction harnesses that retain the fundamental weaknesses of the factory design (full alternator current passing through firewall to ammeter, packard 56 spade terminal corrosion, accessory and battery ties buried in the harness, limited fused expansion circuits, etc) are an expensive solution.
With basic electrical skills and patience you can adapt a color coded harness like Ron Francis or American Autowire and come out ahead in function and reliability.
I would start by laying out your harness on a large sheet of cardboard or plywood in a linear fashion and with tie wraps or twist ties build a layout panel. Your harness was originally made this way. You can then begin to cut apart your old harness wrapping and inspect each circuit and wire. You may be surprised at how good some of it is. Wires that have oxidized conductors or damaged/spliced insulation need to be replaced.
Packard connectors and harness tape (no glue, black vinyl non-adhesive wrap) are available from Terminal Supply and AVeeCo vendors.
I like to go through a Mopar dash harness by stripping the fuse panel apart and removing the firewall connector terminals. I make a layout panel with the engine harness and the other harnesses on the engine side lined up to the dash harness.
I replace all the Packard spade terminals for through-firewall circuits with a Delphi Weatherpack connector except for the alternator which goes to a firewall stud. Terminating the Weatherpack is simple and reliable requiring about $80 investment in a professional crimper. There are a lot of reasonable Weatherpack starter kits out there - Casper is a good vendor.
The fuse panel also gets replaced and there are lots of options depending on how many circuits you want total, and what style of fuse. Some fuse panels also have relay sockets, ground buss bars, and other handy features in addition to the fused circuits. Marine stores and websites have good selections to look at for ideas.
Get the factory wiring schematic out of the service manual and make a copy or buy a reprint. Use highlighters to mark up your schematic to keep track of where you have been.
I have been replacing the stock wiring in Mopars for some time and recently did two with the ISIS Multiplex Power System which is a modern CANBUS-based approach to restoration electrical. It uses networked modules where a Mastercell interprets all switched inputs and send commands over a bus (like USB) to Powercells, one forward and one rear, to switch loads on/off, and at the same time permit soft start/dim, and monitoring of the load for current draw and shorts. This is made possible by solid state (MOSFET) switching instead of relays, or as in vintage Mopars, full current going through switched contacts in the dash.
