UPDATE: Saturday afternoon
Battery was a bit low on voltage check so plugged in the BatteryTender on Friday evening and brought voltage up to spec.
Removed the fuel tank and began a visual inspection and "sniff test" of the wiring harness. Checked all fuses and they're good. I had earlier converted to the blade-style automotive fuses. Did not see nor 'smell' anything to indicate heat damage. Have not, as yet, unwrapped the wiring harness but this is on my high-probability list.
Reattached the battery negative cable. Noted the still glowing OP bulb. Bothersome. Pulled the spade fitting off the OP sender and the light went off. Wiggled and sniffed relays and regulator. Nothing noted.
Replaced the LED-with/resistor OP bulb but the bulb remains lit even with the ignition switch off. With ignition switch off and brown/ground wire connected to the OP sender, I checked the power lead to the OP light and noted a voltage reading of approx 0.66 volts. With OP wire removed from the sender, the voltage read was approx 0.24 volts.
Toggled the run/stop switch to the 'off' position and the OP bulb turns off. Hum... Pretty strange.
With the tank still off the bike but fuel remaining in the carb bowls, I switched on the ignition, pulled the enrichener lever, rolled the dice and hit the start button. Engine fired up without any hesitation and ran as normal.
Quick happy dance, then shut down as the bowls emptied.
Next, I plan to pull off the start/run-stop switch and look for evidence of arcing or any problems inside the switch body. Will run continuity checks as am able to do.
Previously, I have been noticing the need to "Tender" the battery more than the other R65 so I'm wondering if there has not been an undetected voltage leak going on for some time. May be unrelated as the constantly 'on' OP lamp is a new anomaly.
That's the current situation with the bike. Very pleased that the start system functions. Wondering if there may be a smoked wire inside the main harness that has damaged the insulation on the OP wiring thus causing a short to ground... ? As mentioned earlier in this post, I do think it a good idea that I open up the harness wrapping for a clearer inspection.
I remain very open to ideas and suggestions. Thanks in advance for directions in diagnosis.
Monte