1974 Duster /6 rear lights

What exactly have you done to troubleshoot this problem? You have a test lamp? Multimeter? Some alligator jumper wires? Start where it's easy to access. The turn/ stop power goes through the turn signal connector, so that is easy to access right at the column. Better yet, ONE SCREW removes the left kick panel and then you can access the harness connector going to the rear. Measure voltage there

You can download service manuals and aftermarket wiring diagrams free from MyMopar.