I have a 1971 BB Roadrunner in the shop for some wiring issues. Cut to the chase, the harness is pretty much cobbled, hacked and butchered from front to back. I have never had to purchase a complete harness before. What replacement harness would you guys and gals suggest? This is not a numbers matching car so an updated harness would be acceptable to the owner. He wants a reliable driver. Which ones are good? Which ones to stay away from? Ease of installation? Soldering and heat shrinking connections does not scare me, I just don't want one that requires me to build the entire harness if you get my drift. Also need suggestions on getting the cluster freshened up. TIA.

Even if it was in good condition, we are past the 40 year mark - how long is too long on original wiring? I think Classic Industries beats Year One on pricing and sometimes they offer discounts. Should be near 100% plug and play. Some of the terminal ends will function fine but may not be 100% OE correct (wrong color or shape) depending on options. That it what separates the men from the boys but on a driver it’ll look stock and function fine. Save the old harness until the new one is installed, some parts are NOT reproduced as part of the main harness and you may need to build a short accessory harness to complete the job. On a 71 it’s much easier to pull the whole dash frame and wire it on the bench as a unit.

M&H wiring /YO your only choice that should be considered....

What’s wrong with CI’s?

Do they have a stock replacement harness? I looked out of curiosity and only saw universal harnesses.

A universal harness is all I see offered by Classic as well. YO appears to be pretty darn complete and appears to be pretty much plug and play. Thanks for the tip on pulling the whole dash frame and wiring it on the bench.

One thing I learned years ago when replacing a heater core that required pulling the dash.

Take this opportunity to tighten every nut, bolt, screw etc that you can while the dash is out. If your heater box needs any kind of attention (core, seals, cleaned out etc) now is the time to do it.

May as well replace the wiper linkage bushings if they are accessible from behind the dash. Don't forget the pivot seals and gaskets, as appropriate.

Not a B body guy so I may have missed somethings or added stuff not necessary. but just think about what would be easier to do with the dash frame out and you can plan accordingly.

Given the Mopar harness architecture - firewall plug, numerous specific wires & plugs - I'd go with a reproduction harness over a universal one.

A few years ago, I did a complete rewire of a guy's '53 Ford F250, with an upgrade to alternator & 12V neg ground - and used an American Autowire harness specific to that truck.
Nice product, though some wire lengths pre-wrapped in the harness were rally long and the ones for the stock brake switch and a couple others I don't recall now were a bit short.
Labeling & terminals were nice and I'd use them again, but there was time involved on a few things.
Given what the OP is working on, with a FSM things should go comparatively quickly with a dedicated specific harness vs. any other method.
Plus, if it's factory-authentic, serviceability and whatever's in the car's future will be a lot easier to deal with.

I'll echo what Montclaire posted.
Save the original harness and don't ever toss it. Roll it up into a box. When it comes time to do repairs on the YO harness, I can't tell you how useful it has been to have the original. Both for reference and sometimes for parts. Nothing wrong with the YO/M&H - might be the best we can buy. But over time little faults and flaws will come to surface.

For example, here's the ignition run wires at the ballast terminal. M&H after 15 years, and original '67 without their connectors (plastic coverings).
After replaced the terminal with a Chrysler style/Packard 58, the M&H connector was too loose and didn't hold ther terminal in place. But the original connector fit perfect.
Second photo shows original ignition 2 (Start) terminal with its Chrysler (Packard 58) connector and next to it the M&H (Packard 56) connector,
Little stuff. But the little stuff can be important!