ONE brake light does not work

Learn to troubleshoot. Access the turn switch connector where it enters the column and back probe the terminals with either a light or meter. In this case a light can actually be handier. With the thing in turn, whether right or left, you should have "flash" power at the proper terminal. If so, it's in the wiring/ socket/ bulb to the rear. That wiring goes down to the left kick panel connector, down into the rocker trough and back to the rear and UNDER the rear seat, which is a common pinch point.

If you have "flashing" on one side and not the other at the switch, it is the switch at fault

DO YOU HAVE a service manual/ wiring diagram?

Download them free, at MyMopar.com. You may have to settle for Dodge vs Plymouth, or other way around, for some years,