'78 Econoline was trying to start by itself this morning. Yanked the battery cable. It rained overnight.

The starter is brand new.....bad ignition switch? Starter solenoid?

The fuse box seems fine/dry. My wiring overall is pretty ugly, but hasn't been problematic.

Not a Ford guy. So... Solenoids getting a hot from somewhere? Something is grounding out somewheres. I'd be suspecting that ugly wiring
Safety First! have that fire extinguisher handy!

Lucky you were there when it happened ... HIGH fire danger ... Keep the batt disconnected and Id replace the wiring to the ign sys water has gotten in the casing of the wires some where ... may be the fuse box shorting out when it gets wet ... but I would not put a batt to it till you find out what it is .

Rain knocks out my wipers ... lol just when I need it .. some times it works ... always works in hot weather

When I heard it, I was like 'what the heck, somebody's got starting probs' then I open my front door and the thing is cranking like crazy......at least I know the battery and starter are strong lol

So I connected the battery back up (no poltergeists this time), now it won't turn over. I haven't checked the solenoid or anything else yet - what else should I look for before I poke around?

Id start with a multimeter at the fuse box

I'm not a Ford guy either, but I have several friends who are, and back in the day it seemed like those old solenoids were always the main culprit of their issues. I had two different friends that ran big block bumpside pickups (67-72) at the drag strip and they were constantly fighting and replacing solenoids. Let us know if you figure it out.

I got stumped after swapping out the solenoid and ignition switch. I found a guy who makes house calls and we got her running today. There were some wires that had gotten tangled around the steering column which was probably the cause. We're in agreement that the wiring has to be completely redone, it is so Mickey Moused it's laughable..... Dr. House Call is seasoned and works cheap, so he's on board to help out when needed!

We're about to start rewiring, and want to redo/upgrade the distributor - any recommendations ? Electronic kit? Never done one so I'm a little bit stupid.

If you're going back stock https://www.rockauto.com/ is hard to beat. Complete replacements under $50.
If you're going HEI then Summit has 'em for about $175. And they're tall enough to clear any intake manifold changes you might make down the road.

Woof, that's kind of steep. Probably going HEI more than likely........but I can find them for as low as $50 - what am I getting for the extra $125?

$50 is a good price for a complete HEI distributor. Cool.