RE: 1969 Dart Brake Light(s)

Question guys:
I have a '69 Dart with all external lights working accept the left rear brake light. I changed the that bulb twice to ease my mind, but still the left rear brake light will not light up when brake pedal is depressed. All turn signal lights work (front and back); all headlights work, just this left rear brake light.
Is this indicative of a faulty turn signal switch or is the another possibility that I can check before ordering a new switch? Please advise.