headlights are not working . ground issue ? 1973 dart slant 6

Look at the photo you posted of the two ground lugs. L9BK is the common ground for the HL. The H9 wire is the horn. Then look at the diagram I posted of the HL connector. The two blacks comeing out of that connector is the L wire ground. They jumper across so both HL end up grounding in one wire. If you can't find it, cut them off as pigtals, and ground them individually near the HL buckets