What I suggest, and do when building a harness up -
- first, go over the harness with a fine tooth comb and check for corroded connections, split insulation, weak splices, etc. Fix anything you find using quality sealant-lined heatshrink butt splice terminals and a ratchet or hydraulic crimper. Check to make sure it still runs well, then heat all the shrink tubing.
- next, moving from the ends of the harness toward the center, use cheap zip-ties to neatly bundle everything as cleanly as you can. Pay attention to where the harness will need to flex or have extra length to handle movement, i.e. where the harness crosses from the body to the drivetrain.
- next, lengthen or shorten any wires you've found to have a lot of slack or not enough slack to bundle neatly while zip-tying.
- substitute appropriate size fuses for any fusible links or at the very least, crimp in quality quick-disconnects or bullet connectors (of the same sealant lined heatshrink variety) so that replacing a fusible link in the future will not involve hacking up and soldering the harness.
- use dry vinyl harness wrapping tape to wrap all harnesses, again, working from the ends inward so that the tape does not unravel. A drop of super glue between the first and second wraps at the end of a harness branch can help as well. Do not fully wrap the harness where it needs to flex for installation or during operation, as the harness will be very stiff if fully wrapped. As you wrap with dry vinyl tape, clip the zip ties off just ahead of the tape, as they won't be needed anymore and will only make the harness lumpy.
- install split loom, again working from the ends of the harness inward. Wrap each junction or end with quality electrical tape such as 3M 1701, paying attention to the angles so that the tape will be evenly stretched and won't be able to bunch up by sliding sideways and leaving a trail of adhesive residue behind it. The last wrap or so should be unstretched so it doesn't peel off or "flag".
If you build a harness like this you should have no issues with it and it will be easy to work on if you need to add something in the future.
Oh, and the following products should never be used in wiring harnesses:
- scotchloks - need I say more
- duct tape

nono: AMC and chrysler)
- wire nuts - those are for home electrical, not automotive.
- scotch tape, friction tape, harbor freight electrical tape - unless you want to end up wearing half the adhesive next time you work on the harness
- harbor freight zip ties - brittle plastic, fail very quickly in an automotive environment if they don't break while you're putting them on. Good for harness lash-up while prepping to vinyl wrap but that's about it.
I've seen some very clean harnesses built with waxed lacing twine, and done a bit of cable lacing on telco/datacenter racked equipment, but I prefer dry vinyl tape for automotive environments. It's a matter of personal preference, use whatever you like more.
The last full custom harness I built (94 XJ 4.0L/AX15/NP231 with full XJ EFI going into an e-carb equipped 87 YJ 258/A999/NP207 with a CJ7 dash swapped in) started up on the first crank after replacing one fuse and hasn't had a single problem yet. Since the factory disaster lasted 20 years, I expect the new harness to last at least that long. I'll have to take some pics and do a write-up on harness cleanup at some point, now that I think about it.