step by step is going to be hard.

so you still have power inside, just no charging.

I would bypass the bulkhead for now. run a 10 gauge from the back of the alt to the positive side of the battery.

that takes out the bulkhead and amp meter.

then fire it up and start checking voltages.

once you are sure nothing is out of whack there, then you can start checking what gave.

most likely 2 sources of problems.

1 the bulkhead connector itself.
the corrsion builds up there and causes heat and melting. shorts stuff out.

2 the amp meter as mentioned above.

you can pop the bulkhead connector and report back on what it looks like. green and melted guts means it was bad.

you can bypass the amp meter by putting all the wires on 1 post, but won't make a difference till you get power back through the bulkhead.