Wow! I was gone for one day and I have all these responses! Thanks for the information.

If I understand correctly, first the wire from the battery to the starter relay failed.
Then after this was replaced, you were trying to figure out why it would not start. I think this can be figured out. It will help to draw out the wiring to include the voltage regulator and the ignition. I still think its likely alternator or alternator wiring related.

PS. Those Mymopar wiring diagrams didn't seem to quite match what I'm seeing in your photos. Turns out those are not factory diagrams. I have no idea where they got them from - something aftermarket like Chiltons or Mitchels I guess. If its the same as the late 60s, the real diagrams are probably in '71 Plymouth service manual (which is also on that website).

https://www.amazon.com/50-Female-Terminals-2084421-2962447/dp/B0040CU11M

https://www.amazon.com/Packard-Male-Gaug...9BYT9ED6A1SXCMY

cheaper than napa if you are ordering on line.

or del city or
probably a few other places.

I only use napa when I need 1 or 2 and have to have it today.

not sure I would order a new bulkhead connector.
you can patch up or by pass the one you have.

taking it apart and redoing all the connectors is good enough.

Ok cool, I will try to get by without having to get the bulkhead connector first.

"Based on the info so far, I'd start with checking the alternator's battery stud for a short to ground and work back from there."

how would I go about doing this? Would all of the wires have to be hooked up first, or just take off the alternator and have it bench tested?

Sorry for so many questions, this is a weak area for me and I am learning a lot, thanks!

Let me see if I understand the sequence.

First you install the battery and before even turning the key, the wire attached to the fusible link fails. (Not the one with the ? mark.)

You replace the failed wire with the red wire the arrows are pointing to.
When the key was turned to start, the starter turns over but it won't start. The lights do work. Then maybe you put it in run and jump the starter while checking for spark from coil wire to ground?

During this testing, you notice smoke and find the battery and alternator feeds have burned.

The NAPA terminals you linked to shows them to be for 14-16 gage. You'll need the next size up, 12-10 gage.

My suggestion about replace the bulkhead is because I can see more damage than just the burnt cavity itself, Several areas broken due the age, not related with this short.

Since you got burnt the cavities and these terminals are weak no matter what AND the original Mopar alts are poor output level at iddle I would advice consider upgrade the alt for a better output unit ( able to source around 45-50 amps iddling ). This is a tipical failure from stock disposition, poor alts what burnt these packard terminals and overheats everything around. Run the wires straight through the firewall will save the weakness of the packard terminals for the charging loads when reving up a pooor iddle output alt

If you make that you can:

-Forgett the packard terminals since we are telling to buy to replace the ones burnt... no need to buy them. Remove the old wiring from the old bulkhead clean terminals and relocate them on the new one,

-despite the new engine harness plug. If just got damaged the black wire location just forget about that. Clean the rest of terminals thought. Remove the existant black wire at engine harness.

-No need to splice two new wires into the man splice inside the cab. Just run the section between the main splice and ammeter with the same 12 gauge wire or maybe 10 straight to the solice if you want. The new wire to the alt can be attached straight to the ammeter stud. You'll be getting two terminals on black side of ammeter, the one from the main splice and the one from alt. This make just one splice job and also a straight recharging path ( if batt got discharged ) between alt and batt without need to go through the splice, Splice will suck just what needs from amm stud.

This is just if you decide to run wires straight through the firewall instead using the stock disposition. On my thread about the alt upgrade ( the first one I posted here ) I suggest the parallel path to this just because if the stock disposition is still good no need to remove them and you could use smaller gauge in parallel path ( 12 or 10 ) , BUT if the original wiring disposition is already burnt these can be removed and just use the paths out of the bulkhead using thicker wires... ( 10 or 8 )


And I still don't gett how is the fuse link wired on starter relay and I can see it in good conditions not burnt! It should burnt way before this damage was done. A fuse link takes its time to burnt, and allways gives time to some damage thought, but not like this!