whats wrong with my headlight

My 65 harness has a short ground wire to a screw just behind each headlight that serves both lo and hi beam filaments. I got an engine harness from a 73 Dart at PickNPull for making a new harness. Those run a dedicated ground return wire, which seems like a better idea. I don't know if this mod was because the local grounds were problematic or the 73 didn't have metal to connect to (fiberglass front?). Anyway, ditto the advice to check your ground.