I made a large format print of the 520 wiring diagram I found here
and have run through the wires. What I found was odd. In addition to the brake light PRESSURE switch under the hood, there is a mechanical pedal switch (and it looks very factory-ish). The green/yellow wires, which are in the harness just above the pressure switch (where I would expect them) have been doubled back into the cab through the hood release grommet, and then tie into the pedal switch. Ultimately, it doesn't matter whether a pressure switch or pedal switch is used... but the lights still weren't working. So, I buzzed all the bulbs, and they were good. I then took a pencil and used the eraser to clean the contacts down in the bulb sockets. Viola. That was the problem. So... I'm guessing the PO couldn't figure out the problem, and added the mechanical switch (which didn't solve the problem). In any case, I routed the wires back to the pressure switch and yanked out the excess wire that was running into the cab, and all is well with that. Now... on to the next electrical mystery... the green wires pictured in my OP. Any ideas on those? I'm still studying the wiring diagram, but it hasn't jumped out at me yet.
Here's a pic of the pedal switch.