Turn Signal Lights dismantle on 67 Barracuda

OK the original ground path was through the crimped lip of the bulb socket to the cast metal fixture. I once found a similar fixture fault to have a huge gob of solder melted all around in attempt to correct that metal against metal current path. Yep the solder had turned loose, probably a few times given the amount of solder found. I cleaned away some solder, drilled a tiny hole against the crimped lip and inserted a little screw. ( No idea where this little screw came from, just something rolling around in my toolbox ). The screw head didn't touch the bulbs globe, fixed it, hopefully forever.
The type of socket you have in your trunk just might work but... it doesn't have a weather gasket. Make a thin rubber washer gasket? Simple enough.
Another suggestion... There is a mostly plastic 3 wire bulb socket ( 1157 plus ground ) with a gasket that twist locks into a fixture. These were also inside the trunk of many different applications. This type of socket is likely available on the HELP line of part stores too.
You would need to whittle/reshape the round hole in the back of your fixture for the twist lock fit,,, If that hole isn't already too large. I aint tried this, just throwing the thought out there.
Or buy a good used OEM fixture/socket assembly.