I have had a rodent issue before and found online that it is a pretty common problem with newer wiring. Apparently the manufacturers are using a soy based component on the "plastic" insulation that attracts hungry critters. If it was a newly manufactured harness, it may have been nibbled on exposing bare wire. Probably not what happened here but an interesting FYI

Update: I spent the day ripping apart melted wires. I took the steering column and cluster out completely allowing me free access. Someone had mentioned a fuseable link. The fuseable link at the starter relay was still intact but the wire was melted. Bizarre.

Red and Black were the cooked wires. The others around it were collateral damage with red and black melted goo on it but they are still intact. As I took the time to peel them carefully apart, I inspected the other wires and so far so good.

I was hoping to try to replace just the black and red wires for now and see if that would work. Being an original harness, I wonder if those two wires had somehow worn and shorted within the harness? The red wire is completely out, but the black appears to be spliced to several other circuits so I will just cut and splice the new ends (see photo).

Could the ammeter be had causing this? If so, how do I test it before I put it all back together?

As you can see, the only two fried wires in the harness and at the bulkhead are red and black. As I replace these two wires, what gauge should they be?

Do you have a service manual? If not you really need to get one. Are you done checking the harness?

Today I just took it all apart and visually checked everything and completely removed the red wire which had barely any insulation on it.

The black was better but not by much. If the red or black was the culprit, its impossible to tell now based on their messy suicide.

I do not have a service manual (if I do, its buried in my shop since we moved 3 years ago).

I was thinking to test the harness with the test light as mentioned, but I would need the red and black wires replaced before that would work, right?

wiring goes bad from: excessive flexing that work hardens and breaks the copper strands (rare)/pinched insulation that breaks thru the insulation & allows copper strands to dead short to ground (fairly rare)/ poor or no continuity at the terminals/connections over time due to moisture causing corrosion and poor crimping/poor or no soldering when it went together (fairly common over a period of time). lastly open & burnt terminals/burnt insulation/sometimes melted copper strands if enough amperage is flowing which is what happened here either from a dead short to ground (likely) or a near dead short to ground in an electrical component. the flimsy ammeter insulating washers may have let it ground into the ammeter mounting bracket. visual & ohm it, neither terminal should have any continuity to the mounting bracket. Otherwise keep digging. I had a reg full field to where the insulation was melted (not near as bad as your deal) cuz your dead short is worse & the fusible link NEVER opened. A guy suggested one of those colored plastic fused with the 2 male lugs (& carry spares) is a good move, a 30 amper tho other than that on my '66 dart I have had no issues with dead shorting or full fielding.

While you have everything apart, I would take all of the nuts, and so forth on the gauges and clean everything with a brush and Deoxit.

so that splice could be factory.
I set a link for the wiring diagram from the service manual at the top post I made.
Check it out, it will show if that is the case.
IT doesn't look melted rather clamped.

maybe yes, maybe no on the test light.
Those do provide power into the car and back out. The splices go to other circuits to power them up.
But even without them, it would show dead shorts to ground.
If every circuit is dead then you know those were the only damage.
If something lights up then it is time to trace that circuit.

No damage to be done as the test light is the only load and would prevent further damage.

That looks like the factory welded splice in the dash.

FYI: Just checked ammeter ohms and it has no continuity. As far as the test light, let me make sure I am doing it right. Thanks in advance for patience, electrical has never been a strong point for me.

battery ground on.
Leave positive battery off.
attach long wire from + battery to + side of test light.
Start checking circuits (at bulkhead connector?)
Do I need to ground my test light to the chassis as well? or will the negative battery cable do this for me?

I agree, it had the old mopar cloth tape around it. I will fix the black wire ends and retape when done.

I am not sure how to explain that simply.

so test light to positive on the battery. should only have 1 wire on it.
not a meter, but test light.

the ground connected to the battery on your harness. no positive cable connected.

Now you should be able to touch the test light to the positive cable and say with the key on or a door open, (assuming your switch works) and the light should light up. It completed the circuit and is drawing power, but limited to your test light.
Your interior lights shouldn't have enough power to come on. (at least I think) worst case you pop your test light.

Doing this with a meter might burn it out. or blow the fuse and I think you would have to do amps.

Anyway, now if you check any other circuit it should do the same.
Anything that completes the circuit to ground, either by dead short or a switch turned on to ground, will cause the test light to come one.

But you have to be sure you have enough of the circuit there to test.
As long as the engine to body ground is there it should work on any dead shorts to ground no matter where they are.
You can test it by touching the test light to the body or bare block and see that it lights up too.
That means any wiring exposed and touching the body or block will cause it to light up too.

IF it doesn't then you don't have a complete ground circuit and you will have to find out why.
I can't imagine that won't work, but let us know if it doesn't.

That appears to be a factory junction, probably the main junction.
Start by looking at the diagrams showing how the power flows .
Then look at the damaged wires and see what they connect to.

.
Take a picture there as well.
Not neccessarily strange at all. It depends on where the short was, where the power came from (was the engine running?) and where the highest resistance was in the path back to ground. We know there was enough heat at bulkhead to break at least one connection.

It is important to get the electrical diagram for your vehicle. If you don't want to buy, take a look around the web, people have posted portions electrical diagrams here as pictures and there's even some pdf floating around out there. I know that 'cause I was looking at an early 70s Dodge diagram within the past month or so.
The diagram will show the wire gage. It will show the insulation colors. It will show where the wires are supposed to connect. It will show the fusible link or links and there locations.

Again you can use my simplified factory diagram as a starting point. Much of it will be the same or similar. (Differences will be the bulkhead numbers, link location, and of course the alternator will have a ground wire to the regulator.) Another difference may be the wire sizes and some of the colors.

http://www.mymopar.com/index.php?pid=27

diagrams for a 71 rr. near the bottom of the page.

http://www.mymopar.com/downloads/1971/71SatelliteGTXRoad%20RunnerA.JPG

engine side.

http://www.mymopar.com/downloads/1971/71SatelliteGTXRoadRunnerB.JPG
under dash side.

Its interesting that the ammeter does not show signs of damage at its connections. The only concern will be if the shunt was damaged.

I think an ohmeter may be the best way to look for high resistance and poor continuity in the wiring. You can also use it to check for shorts to ground.

PS. Figure out what #18 on the bulkhead connects too. It's melted insulation suggests it got too much current. If yes, I'm seeing that right. Then its a clue where that excessive current was flowing too, depending on if the engine was running or not.
If the engine was running, then that will explain things too.

Andrew, Thanks. Then the big question is whether the engine was running.

engine was not running. I just hooked up the battery and the smoke show started. No key in the ignition, nothing.

#18 on the bulkhead is connected to the alternator.

#16 was the red wire coming in hot from the starter relay.

OK. There you have it. Now you know where to look. Right?
If not, look at the diagram and ask yourself why would power be flowing through #18 to the alternator.
I'll see if I can hot-link it direct, but my host service may not allow it. If not I'm refering to Nacho's diagram in this link.
http://www.heritech.org/cuda/Charge.html

(yes. they've made it hard to hot-link)

Ok, I am looking at the link and I see the path is should take. But, shouldn't the alternator be hot all the time with battery connected? What would cause it to draw that kind of power with nothing turned on.

The ammeter is a link in that circuit. So what would be the weak link that would cause that to fry? headlight switch, ignition switch, or something with the fusebox..... Would a faulty ammeter cause something like this? The wires were cooked to and from the ammeter, but not the ammeter itself.

I should also add: after I replaced the wire from the starter relay which was fried (at the time I thought thats all is was), I was able to turn the headlights on and off. The key worked by turning over the starter, but no spark to coil. With the battery connected, the R side park turn signal was on continuously (not blinking) as well as the blinker indicator (also not blinking) on the dash.

I have to work tomorrow but I will do some more investigating and wire repair on Monday. Thanks so much for all the help, I really appreciate it guys!

eightlitermopar

I'm going to have to think about that (what you just wrote) too.
While you were writing that, I was marking up one of the drawings.

To the first question. shouldn't the alternator be hot all the time with battery connected? Yes.
The wire to the alternator will be at the same voltage as the battery.
But, there will be no power flowing in that wire because there is no place for the current to go. The power only flows when there is a lower voltage, idealy ground, zero voltage.

So my first guess (illustrated here) is that the alternator wire was somehow connected to ground. This could have been touching a ground wire, the chassis, or internal to the alternator. Use an ohmeter (or a test light) and see if that wire is grounded.