Tail Light Issues

1970 318/auto Dart Swinger standard dash/cluster

I'm having some tail light problems and I'm not sure if it's tied into the signal switch, the flasher, headlamp switch or none of the above. I'll try to give as much detail as I can. When I mention "tail filament" I'm referring to the tail light and not the brake/signal light.

Left signal on with headlights on:
Left tail filament stays lit.
Left signal/brake filament blinks brightly on and off.
Right tail filament barely glows.

Right signal on with headlights on:
Left tail filament normal
Right Tail filament blinks dimly
Right signal/brake filament does nothing

Brakes on with headlights on:
Left- both filaments on normal
Right- all off

Brakes on with headlights off:
Left- Brake/signal filament bright
Right- only tail filament glows dimly

Headlights on only:
Left tail filament normal
Right tail filament about 2/3 as bright as left

Emergency Flashers on:
Front normal but fast
Rear nothing on either side

Headlights:
Testing with plugs unplugged in trunk
Left black tail light wire: 11.7v
Right black tail light wire: 11.7v

Brakes on:
Trunk Left green wire- 11.7v
Trunk Right brown wire- 0v
Green wire at turn signal switch under-dash column plug- 11.7v
Brown wire at turn signal switch under-dash column plug- 0v

The right stop/signal filament does not light or show voltage under any conditions.

That's as far as I've gone so far. I also changed out the right rear lamp. The wiring is all non-molested.

Thanks for any ideas.