turn signal working intermittedly

Where the park/turn fixtures are made of metal and mounted in metal, there isn't an actual ground wire for/to them. Those bulb sockets are crimped into the fixture to create a chassis ground path. You will find a single ground wire attached to the radiator support that branches within the harness and grounds the sealed beam headlights. Let's not mention the headlights again as they are irrelevant.
So.... you have park/turn fixture(s) on one side of front that don't work. Finding a fault in the positive side of the circuit is the fun part. First bulkhead connections then inward to hazard switch, etc... good hunting