Reversing Battery Polarity

[VWGirl]

It's almost as if I have to wait for it to die completely so that I can fix it, 'cause otherwise it fixes itself in a second.

I've been there, about electronics troubleshooting.
The trick was to help it go bad, heating with a hair dryer at potential culprits.

The problem is it's such a slight hiccup that I don't know that I would notice it sitting still. Since it happens so infrequently, I could be sitting there for hours trying to make it happen just to have it happen once on my next 1000 mile trip.

What I need is my own personal Colin to ride around in the back of the bus checking everything as I'm driving down the road! lol

[twinfalls]

This is very difficult to catch.
Among many causes, it sounds like a wiring trouble.
The reverse battery has put extreme amps in the wiring. May be it got so hot that some wires melted their insulation at some places. So now you get intermittent short shorts.
Changing harnesses may get you in deeper trouble.
Check again the actual wiring at the ends where it is crimped for sane insulation. Plastic connectors melted around some spade connection; These are potential hot spots.
Terminals at fuse box, 8 points connector in the bird's nest under the instruments cluster.
I would look very closely at unfused 12 volt wires ( those did suffer from the reverse ). All #30 terminals.
May be an EE analysis at the wiring diagram to identify wires that did suffer from the reverse...Based on the alternator diodes that got forward biased allowing huge Amps.

[VWGirl]

Sounds like a good theory and all, but this intermittent issue started about 5 years and 30k+ miles before the reverse polarity issue.

How would wires suffer from reverse polarity? If I took the wire and connected it the other way, it would still just be a wire. There is no positive and negative end of the wire. The components are what will suffer.

So actually the current issue has nothing to do with reverse polarity, it should be started in a new thread now :)

[twinfalls]

How would wires suffer from reverse polarity?

I had twice the reverse polarity scene.
First time I was helping one to jump start his van from my Westy.
He did hooked his battery reversing the cables.
A huge spark. I had a dead battery a week later. I thougt one had to be real dumb to make such a mistake.
Second time, I did it all by myself, jump starting my Westy from my VW Golf GTI. Insisting in my stupidity, revving the Golf engine.

The cable clamps got so hot, insulation melted and burnt at a clamp handle, some copper wire strands got cut.

Such a reverse is like shorting a 24 volt battery. Yes, two times 12 volts.
Shorting a 12 volt car battery can make current in the 400 Amperes range.
That is huge, enough for arc welding and exploding the battery.