[Mechaniker]

Hi there, I'm new to pelican and Porsches but not to owning old cars. I recently purchased a '85 Carrera 3.2 that has an intermittent issue with the tachometer, and I'm looking for some input from folks who might have had a similar problem, or might know what the problem is. The car has about 95k miles.

Symptoms:
The tach usually will not work when I first start the car, the needle just rests at zero, though the shift light appears to work normally. After a minute or two it will usually start to work normally, but periodically and randomly it will stop working again over the course of a drive, sometimes for just a minute, but other times for several minutes. Again, the needle drops to zero but the shift light continues to work. One other observation is that when the tach acts up, it will appear to rest at zero at lower/cruising RPM 1-3k rpm, but if accelerating at higher rpm, maybe around 4-6k rpm, I will notice it lift slightly above 0 rpm, almost as if it's severely out of calibration.

Diagnostics so far:
Since the shift light still works continuously, it doesn't seem to be a major connection issue. I had a couple of the gauges pulled out the other day when I was tightening my wiper motor down and I checked for loose connections anyway, but nothing seemed out of order. The car has an Autothority chip, which I suspected might be the issue so I swapped in the stock chip, but the problem has persisted.

Questions:
Has anyone else had similar problem? I've read about "bouncing tach" issues attributed to failing alternators, but that doesn't seem to be the symptoms I have. What should I check next? Could the tach itself be at fault?

Thanks in advance!