OK, something strange developed in the last couple of days.
Engine temp gauge jumps erratically and intermittently.
At the same time, the headlights and dash lights tend to flicker.
Once in a while during this phenomenon the engine hesitates.
Sometimes the glow plug lamp will also flicker.

I'm thinking this could be a ground issue on the instrument cluster, or maybe a voltage regulator issue. Has anyone else experienced something like this, or have any input.

An electrical schematic would also be helpful, if someone has one.

1980 300SD W116. - 360,000 miles and still going.