74 Dart Swinger Front Running Light Issue

Check the connector at the base of the steering column that comes from the turn signal switch, check the turn signal switch (unlikely) and the bulkhead connector.

My guess is the connector from the turn signal switch.

If it was the bulkhead connector, then the 4 ways would not light in the front.

If it was the headlight switch, the running lights in the rear would not work.

If it was the turn signal switch, the directionals would not work in the rear.

Last (obvious) spot is the connector in the steering column. There is a wire that goes to the "body" harness and that carries current to the rear - that appears to be working. There is another that goes to the bulkhead connector and then to the front lamp harness. Since the 4 way works, it is likely the connector or (remotely) the turn signal switch.

Hope that helps!