I've managed to disentangle and separate the mess at the fusebox and under the dash. Found plenty of PO hackage, and more burnt wiring. I also discovered a few things about the factory harness.

The headlight switch SHOULD have four connections: power in, parking lights, lo-beams, dash lights. You could get away with three, and merge the lo-beams and gauge lights in the harness later. So, why are there FIFTEEN terminals on the headlight switch, with several connections with doubled up wires on them? There's like 20-30 wires there. OK, for ultimate reliability, I suppose you could run a wire to each light individually, plus the gauge lights and power, but that's still only 10 wires...

I think some of the final assembly (maybe a dozen crimped connections) was done after the harness was on the car. Some of the assembly must have been pretty challenging. I can see this in a low-volume setting, and it's certainly how I'll make the replacement, but to make around 100 cars per day in this way is pretty amazing.

see that's why I like these cars so much, people's souls went into the production of this fine automobile.....this is before the time of robots.

Car assembly is not the same today. I've been to the MB factory here in Alabama where they make the SUV. It really is a big machine that people run around feeding parts and supplies to, while it holds and spins and welds and bonds and paints and spits out toasters. Oh, wait, I mean SUVs. I guess it is a "quality" machine (I've never driven one, but have driven a 2003 340 that was very nice), because it uses better parts. Really, parts made with thicker stampings, or maybe just tighter final inspection or something. But anyway, no real hand assembly of cars. Just a big collection of automated processes. It made me realize how you can't really reassemble one after some kind of "restructuring". But I think it must make mire investment sense to put the money into the design and construstion of the device that builds the product- toasters or wharever.

Couple of questions, are you planning on using a modern use box? If so how many terminals are you going to use? Are you going to use higher capasity wire that the orginal (I assume you are) and if so what gauge?

I have been thinking of doing this also and I am very interested in your progress.

you are going to take pictures and document your progress so that we can copy you in the future???

on a sorta related note, I installed a new Engman fuse box assembly today, installation was easy...only issue I had was that I had a problem installing the screws to attach the plate to the factory mounts....it had to do with all the wiring getting in the way...so I machined 2 pieces of 1/2" thick Delrin to act as spacers and mounted the fuse block assembly just a little bit lower....it still is flush enough that I don't come close to hitting it with my feet.

I'll take some photos once I start assembling the new stuff. Right now, all you can see is a dirty interior with wires EVERYWHERE, which may be a nice "before" shot.

I'm not actually interesting in adding more capacity. Instead, I'll be using substantially fewer wires, for a simpler and lighter harness. I've removed some accessories out of the loop already (both fresh air blowers), and I'll probably not add a radio or any other power-sapping devices. I ordered a set of LED taillights from Waytek. We'll see how they work out.

I will be using ATO fuses (the newer blade-type jobs). I won't be using any of the stock round relays. Common cube relays are cheaper and easier to source. There are solid-state relays available, which have major reliability advantages, but I've only seen them at pretty high prices so far ($30 each).

Couple of photos:

This is the mess that exists behind the dash. There's about 10lbs of wire there.

Here's an example of PO hackage: this relay is NOT OEM. It's tied in directly at the steering column, and took some doing just to fish it out. No clue what it was supposed to do. The white/black wire isn't part of the OEM wiring, but disappears into the steering column harness. The orange wire with the pink connector goes off to nothing.

The wires dangling from the steering column with the blue insulated spade connectors are from the turn signal/high-beam switch. This is a '71, so there's no stalk on the other side. The wiper/washer switch is on the dash. The connections out of the ignition switch all lead into a connector very like the connectors on the relay board. I've disassembled it in this photo.

It is (just) possible to remove the harness from the car without cutting any wires. This will really try your patience, however. All of the harness wires must basically be pulled towards the fusebox. The wires in the front trunk section need to be disconnected at the lights, wiper, and front blower, then pulled down through the scuttle to the fusebox. The connections through the center tunnel have to be pulled forward through the tunnel.

I'd really advocate NOT removing the complete harness unless you have a really good reason to (like you're going to acid dip the tub). The harness isn't split up into convenient sections, either, so if you feel you have to remove a section of it, you're basically looking at removing ALL of it. For the most part, wire itself doesn't go bad. Insulation does, and if it's very brittle, the insulation will usuall crack and break away from the wire. End connections also corrode, but can usually be cleaned up more easily than they can be replaced.

In short, do not do what I'm doing now. I'm completely insane, and will very probably be following Miles to goat-herding land any day now...