More vehicle info please. That battery tray looks pretty bad, what kind of shape is the rest of the car in.
The wires might not be your worst issue.
What are your long range plans for the vehicle.

Last edited by Rudi (5/04/2020 8:19 PM)

Also check the other side of the firewall, I'd be surprised if the damage was only in the engine bay.
How far up the harness did it burn? Do the wires look burned at the firewall end?

Last edited by 50vert (5/04/2020 10:51 PM)

My question was to find out if you want to keep the car stock or to do modifications that need more than stock wiring.
If the rest of the wires in the car are in the same condition as the one you pictured, you may have to replace all the car’s wiring. If that is the case the cost involved will be far greater than going to a complete replacement such as the one that American Auto Wire sells.

I've heard good things about AAW.  I elected to just use replacement harnesses and modify the harnesses where I needed.  I added relays for the headlights (that's basically a must if you want to use modern bulbs), added an electric fan, added modern gauges, added a modern audio system, and will soon be adding power windows.  The thing I like is that the circuits I didn't touch still have all the stock color wires, plugs, etc.  This allows me to easily use factory diagrams and schematics in future troubleshooting.  If you plan to add a lot more electrical items now or in the future I would suggest both upgrading your alternator to a 3G, and consider adding an auxiliary fuse block to make tying in accessories clean and easy. 

I'll second John's advice to use NPD as a supplier.  I've never been unhappy with them and I've bought parts for both my '67 and my '89 from them.  I actually found a couple of NOS parts there at reasonable prices.  With the closing of Mustangs Unlimited they will now be my go to supplier for the '67, and I'm sure I'll buy more stuff for my '89 there too, though for late models LMR is really hard to beat if they have the parts you're looking for. 

As far as abilities, you'll learn.  That's what we all did.  Electrical is typically the least intuitive for all but those who have an electronics background.  Just take your time, be patient, and ask for help.  The good news is these cars are very simple electrically, so they are good to learn on and easy to troubleshoot. 

Even though the AAW kit is a major undertaking it could be the best route. 
 The kit eliminates all the decades old brittle wires, impossibly hard connector plugs, corroded bulb sockets, worn out ignition, headlight, wiper switch etc.  One or more, or all of those will eventually cause you grief. the kit also comes with a relay bank for headlights and other accessories.
As for colour coded wires, it's a non issue, each wire in the kit is individually marked for it's function and  the wire diagrams from AAW are in techicolour,  far superior and  easier to read than the microscopic black and white schematics in the Ford shop manual.
 All in all the AAW kit is not difficult just time consuming.
 Also note the AAW kit does not support an external voltage regulator, you will need a 3g Ford or a single wire alternator which as well a great upgrade.

If you want to stay stock, look at;  midlifeharness.com
 They have a good reputation on Mustang wire harness retoration.

Randy is The Man for under dash wiring. He doesn't recommend re-working under hood wiring.
For them, buy new, I think the Alloy Metal brand is the best. NPD has the brand.

My advice would be to get the correct alternator harness for the car.  That's your best starting point.  Its supposed to plug into the main harness.  I would not change that.

After that, now that you are starting where you would have if the car didn't have a hacked up electrical system, I would advise converting to a 3G alternator.  This is especially important if you plan to add modern conveniences to the car like a better stereo, power windows, etc. 

There are alternators billed as being "1 wire".  Frankly they don't work terribly well, and 1 wire is really a misnomer.  Here's a link to a good wiring diagram for the conversion:

https://www.stangnet.com/mustang-forums/threads/3g-alternator-conversion.802741/

That's an old style externally regulated alternator.  Not the original, which would have been an Autolite.  They were ink stamped on the side originally. 

I'm trying to figure out what the wire butcher did to that harness, but as his lack of skill/knowledge leaves me stupified I'm going to stop. 

I can tell what the wires are supposed to do.  The wire missing a ring terminal with the rubber hood on it was for the red post on the alternator.  That's the primary charging wire.  The smaller wire missing the ring that has the large rubber cylinder molded onto it went to the other terminal with the plastic ring.  That's the wire that goes to the regulator.  The one with the large ring is a ground that should go to the block where the ground cable bolts from the battery.  That fourth wire is also a ground that goes to one of the alternator case bolts.  Do not connect it to the stator terminal or the car won't charge (yes, I learned that the hard way as a kid). 

The three wire molded plug should be for the alternator harness.  Here's the right alternator harness for your vehicle:

https://www.cjponyparts.com/cj-classics-alternator-wiring-harness-usa-made-without-tachometer-6-cylinder-v8-small-block-1967-1968/p/WALT4F/

I'd just buy that and install it correctly and not worry about what daddy dip#$%^ did before you.  I definitely wouldn't try to copy his hackery on your new harness.