I have a 1983 MB 300D with a few electrical issues:

the clock doesn't work
the rear defrost doesn't work
the lights on the center console don't work
the radio turns on but no sound
the seat belt alarm does sound

I've replaced the center console light bulb - its still doesn't work
An auto glass shop tested the rear defrost - it works but not via the switch
I've verified the radio wiring and connections - the speakers work

Is there some commonality here that could be causing all or most of these issues?

TIA,

JWJ