[PeteKz]

Mark, problems like this are usually caused by poor grounds, or sometimes by wires with insulation that has rubbed through and is causing a short circuit. After 50+ years, one or the other is likely. There are lots of similar discussions in other threads.

Do you have a wiring diagram? If not, first step is to get one, either by copying one that someone has posted in these forums or somewhere else online. Better yet, get a printed version from one of the online vendors. Then you will have to start tracing circuits with a volt/ohmmeter. There aren't any quick and easy answers, as you should know from having replaced several parts already.

Speaking of the parts you replaced: Did you use known good replacements?

One other thing to do at this age: replace your fuses! These old bullet fuses have a small strip of copper or tin exposed to the air. After many heat cycles and exposure to moisture, they develop cracks in that strip that cause intermittent or strange electrical problems. I have solved weird electrical problems by simply replacing the fuses if they are 10+ years old. Over on the Mercedes List, we call this the "Marshall Plan" after the distinguished gentleman who advocated it.