Got a crazy Starting Issue! ........I mean nutz!

So just picked up a 75 Dart with 318.
Its a semi basket case that runs ok.
Problem is it starts when it wants to.

Symptom:
Will start one day then the next I have absolutely no power to anything. Nothing works not even the emergency flashers.

What Ive tried:
Pulling hair out while screaming........that did nothing.
Fake Crying while pounding on whats left of the dash and telling her she would start for the PO why not me!!!........still nothing.
So I got serious.....

1. Replaced battery with a brand new one.
2. Replaced Starter Solinoid (sp?) This worked for awhile.
3. Moved wires around under dash while Wiggling key, shifter etc.
4. Traced power to Fusable link. (getting power)
5. started checking grounds - Battery to starter ok, Block to firewall is there and
visually looks ok.

Then things got into the Twilight Zone (you younger readers might have to google that to know what I mean :) )

I left the running lights on by accident during one of these no start / no power to anything tantrums. Went to do something else, and after awhile noticed the running lights were on. So hoped in it, turned the key and she fired right up!
What the hell?
Ok, so thinking this was just a coincedence ive tried it every time it does it.
And 4 times now it has started if I leave the lights on. It takes about an hour of sitting before it will start.
I can leave it for days and nothing works to try and get it started. Leave the running lights on and sure enough she fires up. WTF?

This last time I left the lights on after it wouldnt start and ran the battery dead. So I hooked up my portable starter and sure enough it started.
But.......
It would only run if I had the battery charger connected. Once I took it off it would die. Tried it 3 times and it died every time.
I also noticed the negative side of the battery sparks when I connect the charger.


Sooooo.....were the heck do I go from here?
Ive read the MAD Ahmeter bypass article. Should this be the next step or should I start somehere else?
I thought it might be a short but ive left the car sitting for more than 8 days at a time and it always has a good battery.

Maybe its the ugly side pipes? Would you want to go anywhere with those things hanging off your side? Me neither!

Thanks in advance for any insight!

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