After a few attempts. I traced power down to behind the bulbs with the lightswitch out. So the rear running lights should work.
Still no rear running light. Replaced bulb with one from my 1959 , same thing.
Ground should not be an issue cause blinkers and stop light work as they should. If I switch the wires , I have no blinkers and no brake lights but the running light works but too bright.
I don't know.