Powder-Coated Poor Ground

It sounded like the standard broken string ground problem. An unpleasant hum from the guitar
that didn’t quieten down when I touched the strings. If I touched the metal body of the input jack,
things got quieter but no effect when I touched the strings.
Double checking with a resistance meter confirmed there was no path from the strings to the
ground/sleeve on the output jack.
Internally, all looked ok. There was a ground wire from the jack to the pots and the switch. And,
there was a wire from the back of a pot disappearing into a hole in the body that aimed towards
the tailpiece post. It looks like the string ground is in place.
Back to the meter and something interesting:
The metal bushing that the tailpiece screws into… There was continuity between that and the
output jack ground. Still none from the post or tailpiece or strings, though.

Turns out it’s the powder coating on the black hardware. It was acting as a pretty good insulator.
You can see the inside of the post mount on the tailpiece above. It’s nicely coated with black
stuff. Same goes for the tailpieces themselves.
Scraping time.

I scraped and sanded some of the coating off from the mating surface of the tailpiece. I did the
same for the posts.

Also, I cleaned some coating off the post threads and even from the holes in the tailpieces
where the string ball-ends contact.
After that, all was well.
This is something I’ve come across a couple of times now. It really seems like something that
manufacturers should have cottoned on to but, that’s why we get the big bucks.
Incidentally, I’ve seen similar problems with those weird colour-coated bass strings. Those
things that you can get in red or black or whatever. The coating can insulate them and cause a
similar grounding hassle.
Worth filing this away in the weird electrical troubleshooting card-file of your mind.