[Early_S_Man]

Jim,

Is the car a Targa or Cabrio?

This sounds like a serious moisture problem in the passenger compartment has gotten to the wiring harness or ECU connectors. My suggestion is to pull out that seat and be prepared to go through and pull apart every connector ... do the Q-tips & 9% vinegar, distilled water, compressed air dry, followed by 91% isopropyl alcohol cleaning treatment, followed by testing [when the gauges are fogged up] to be sure the problem is gone, then coat all of the connector pins with Dow Corning 4, 111, or 112 silicone grease.