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

Well you need to do some actual TESTING, not guessing.

FIRST if you do not have such, wander over to MyMopar.com and download both volumes of the 73 service manual, and while there, go to the wiring section at MyMopar and download the simplified aftermarket diagrams, which can be easier to follow

SOME OF those manuals got there because of some of the guys right here!!

Ammeters and the ammeter circuit can be a big problem. Read this article to find out the why

http://www.madelectrical.com/electricaltech/amp-gauges.shtml
PART OF the reason your tail/ park/ etc lamps are working is that the headlight switch has TWO SEPARATE power sources

The power for tail/ park/ instrument lamps comes from a fuse in the panel.

But the HEADLIGHTS ONLY power comes direct from a splice in the black ammeter wire a few inches from the ammeter. That wire goes to a different terminal on the light switch, which has a circuit breaker built onto/ into the light switch.

When you pull the HL knob all the way out, the HL power goes down to the DIMMER SWITCH (as mentioned above. It is a simple 3 terminal, double throw switch. This means that with the HL switch "on" there are always two terminals of the dimmer that should be "hot"

If you have power to one terminal of the dimmer and no others, and operating the switch does not change things, then the dimmer switch is bad. If you have power at two terminals and no lights, the trouble is out in the engine bay

If you have no power at all at the dimmer, you have problems up under the dash, time to pull the light switch, and probably, the cluster

ENGINE BAY: After headlight power leaves the dimmer switch, high and low beam power goes out on separate wires through the bulkhead connector, around the fender to the headlights. Often, the headlights are BOTH grounded through ONLY ONE screw. Start by running along that harness and checking for ground screw(s) and making sure they are so

It is not unheard of that headlights can BOTH burn out!!!

If you had power at the dimmer, go out into the bay, and using your manual/ diagram, probe the bulkhead connector for the head lamp hi and low beam and see if you have power there. If so, move on to the headlights themselves