Troubleshooting help

[SS317]

Ok guys,
I just got the old girl up and running again so I can use her as a daily driver. I was going through things and ended up replacing the starter (it was weak and grinding) and the alternator (bearing shot and barely producing a charge).

Before I replaced all of this stuff early morning a couple days ago I pulled out of the driveway and lost all power, headlights, radio, engine died. Very strange. Within 10 seconds it comes back and I restart and park it at home for the day.

This weekend after replacing all the above stuff I drove her around the back roads hard trying to see if she will die again. I could not get her to duplicate the problem.

This morning I start her up and leave. Halfway down the on ramp to the interstate it does it again. Lose power, all lights, radio. I pull over, and call wife. For grins I put on my battery jump starter and notice the battery is a zero volts. Nothing, Nada. I run home and get a backup battery I have for the camper to try and get her home. Hook it up and she starts like normal. I'm about to drive away and before I shut the hood I notice sparks aft of the starter. I quickly unhooked the battery and pulled her home.

Tonight I get home and try to find where the sparks are coming from. I crawled under the truck and looked all over the starter area. I don't see a thing. I hooked up the battery from the top and could see some sparks but can't pin point the exact spot. I don't have a helper until this weekend to have someone connect the battery while I'm under there.

What could be causing this short? I have new wiring throughout the truck, kits from Classic parts, and the start wiring is very clean and precise. I wire airplanes for a living so I know wiring pretty well.

Where could this short be? There aren't any wires around there and I can't find any burn marks. Could the starter be shorting directly to engine? This only happens when the battery is hooked up. Has anyone seen anything like this before?
Cheers.