EZ wiring tail light circuitm

Most everything on these classics uses a daisy chain of metal to metal contacts for a chassis ground path. Most bulbs with metal base in metal sockets in metal fixtures included. Front lamps mounted in a plastic grille require a ground wire.
Headlights require a ground wire. Those bulbs in the inst' panel dont have the metal base and are in plastic sockets so one would think they require a ground wire. In fact they are chassis grounded too, metal inst' housing which grounds to the metal dash via mounting screws.