For these cars, there is a turn signal - self canceling "switch", which is located in the steering column. There is also some additional wires provided if you have cornering lights. Here is an general example.
MD2085 - 1970-82 Chrysler, Dodge, ,Plymouth,; Turn Signal Switch; 11 Wire Style; Car & Truck; with Cornering Lamps
The plastic material of the switch over time becomes brittle and the self-cancling feature will not work. A previous owner may have replaced it with a "Standard" switch that did not have the additional corning light wires. I found this on one of my previous cars.
From my 1969 Chrysler wiring diagram - the LH corning light is a light green colored wire, and the RH light is a light tan - brown.
The connector to the switch is white - clear type color and located under the dash at near the base of the steering column, which them travels to the engine compartment.
With a meter I would check to see if you are getting 12 V at the green and tan wiring connections with the key turned in the "run" position and the signal activated. It will be a steady 12 volts - not flashing like the indicator lamp / bulb. You can then check for 12 V at the connection located at the back of the corning light assenbly in the wheel well.
Another area to cross of the list is to confirm the grounding path - circuit - wire to each of the light assembly's in the fender is good.
Over age, it has been my experiance the bulbs and the contact to the sides of the spring twist bayonet connections get corroded - gummed up. I would suggest pulling the corning lighting assembly out of the car, clean it all up, and run a jumper wire to a 12V source like the battery to check the wiring from the connection to the lamp holder and bulb. Since you have gone this far, replace all the bulbs with new one at this time. ; )
Here is a good source for bulbs at a reasonable price.
https://nationalmoparts.com/product-category/c-body/electrical-parts-c-body/lights-c-body/
I so enjoy turning on a dark roadway and seeing the corning light doing it's thing - its classy.
Hope this helps.
