Hey loglat,
I'm wondering, if when you pulled the panel you might have pulled the turn signal switch (TSS) connector loose, since it ties into the harness right there as well...
behind and just below the support brace.
This might sound like a silly question, Did you disconnect the battery before pulling the panel?
I keep going to back to the TSS, because all of the problems you've described so far can all be caused by a bad TSS.
Especially since you mentioned that the flasher units weren't making any noise. The power feed for them comes from the TSS
The brake lights, turn signals, e-flashers, instrument panel indicator lights all go through the TSS.
It doesn't take much to burn out a TSS... I spent nearly a month rewiring and repairing connections that the PO of my bus "Olde Skool" had butchered when it was the TSS all the time...
It took that long to fix the bus, because there isn't a wiring diagram for it anywhere in the country...
KaptnKA

S