I was going to suggest trying to trace things on a wiring diagram, but the diagram I have of a '71 sucks. But then I went to my '74 diagram and struggled with that one too, so must just be too early.
Have you checked for missing/bad fuses?
Headlights won't work without the dimmer switch on the floor. Is that plugged in?
Best I can tell, looks like the turn signal switch is pretty important in the function of the lights, is that still plugged in?
Best I got. Maybe Mattax has better/more ideas.