Wonky cluster readings on temp and voltage

[shinrai]

Some days my gauge readings are fine for temperature and voltage. However there are days when the temp reading is waaay high (red) and the voltage is low (<=12V). However sometimes when I go over a bump everything comes back to normal. I'm thinking a ground short somewhere. Anybody seen this before? Any ideas on where to look. 1988 944 NA.
Many thanks!

[wild man]

Bad connections, including grounds. These features are pretty much standard for these cars at this point in time.

[Techno Duck]

Check this thread for ground point locations.

Late interior groud point locations

[nynor]

replacing the regulator at the alternator fixed a lot those problems with my car.

[shinrai]

Barely made it home in the '944 today. While I was driving the temp sensor went into the red, the volt meter went to ~11V and the oil light came on simultaneously. The Engine also went low on power (like it was running on 3 cylinders). I pulled over and shut it off to try and reset the oil light. When I went to start it it wouldn't even turn over. I waited and pulled out my CAA card and after 5 minutes I tried starting it again and voila! it started. The needles were up to normal again and it ran fine. 10 minutes later same problem but I kept it running and made it home.

I pulled out the regulator and the brushes looked fine. I also pulled the main engine ground at the bellhousing and it's somewhat split and corroded so I'll replace that first. This corroded cable might explain the no-start but would that also cause the lack in power?

It's charging at 13.5-14 V and the battery is good (all measured with a multimeter) but is there a possibility of an intermittent overcharge out of the alternator that could be causing this? It's getting frustrating chasing this gremlin