wrote: (clip) Possible to wire to cause the single
filament to be "On' as running light, then flash as a turn signal?
^^^^^^^^^^^^^^^^
There is probably a relay that responds to your turn signal switch,
diverting power from the running light, through a flasher unit to the other
filament. Maybe you could use this relay to insert the flasher unit in the
circuit leading to your new mirror lights.

If it's not done with a relay, you should still be able to use the existing
turn signal switch to send power through a flasher unit.

One possible problem: turn signals are generally a heavier, brighter
filament than running lights (or what I call parking lights.) The flasher
may not work properly with the lighter load.