Dodge Monaco -75 rear brake lights not functioning

Hi

Problem with Dodge Monaco -75. Rear brake lights have stopped working. (Can not tell when, this is my fathers old car...)

Anyway. Symptoms are as following:

Brake light switch is working. Blinkers? are working, as well as other lights.

There seem to be some relay or more electric involved?

Questions:

Does someone do have electronic schema for that model?

Does someone guess, what might be reason for this kind of behaviour?

Regards, Juha