Although a wiring diagram would be great to help trace wiring. Your Turn signal and Brake lights would be on the same circuit (wires) to the rear.
Your Tail lights/ license plate light would be a separate circuit and you could trace from the Head light switch.
Somewhere you have lost a feed to the rear if your front parking lights are working .
Found this wiring diagram for an 1963 -880 Dodge , which they pretty much are the same the way they work. In this case its a Black wire for the power for the tail lights, Brake/turn use the same ground with the tail lights ,so that is OK.