While installing new underseat packs (about which, more later) on my Tour Easy, I discovered a bight of PTT cable had been touching the top of the chain:
The gentle ripples to the right of the worn-through section seem particularly nice; you couldn’t do that deliberately if you had to.
This section of cable should have been taped to the upper frame bars. It’s hidden under the seat, just in front of the rear fender, and between the under-seat packs, so it’s basically invisible from any angle.
Soooo, that probably explains a bit of the intermittent trouble I’d been having with the PTT switch, although most of it came from the corroded switch contacts.
Rather than replace the whole cable, I cut out the eroded section, spliced the conductors, and taped it firmly back on the tubes.