dash wiring diagram 74 duster
I know this might be a stupid question but have you tried turning your headlight switch or replacing it?
my dart has an issue at certain points in the dial. if you move it just a little they will go off. if that doesn't work I would get out the test light and test the switch.
there is a diagram in my haynes manual but they suck. I did like the ones from chiltons if you can find one of those. I used a chiltons when I did a motor swap in a BroncoII and they had better all around diagrams.