Hi All - I’ve read through (what seems like) 100s of “tach problem” threads, and I haven’t found anyone with this particular problem yet. My tach has been working flawlessly since I got the car a year ago. Two days ago it decided to basically start showing power on at 1500, idle at 2000 and stops advancing at about 3800. It does advance smoothly with the increase of engine speed - doesn’t jump around or just sit in one place or peg itself at 7000 (like all those other threads I’ve read). It did do this once before for just an hour or so, then went back to normal. No such luck this time. Most threads suggest checking the filter that sits between the distributor and the tachometer...tested (no issues there). I also checked the separate wires by disconnecting the red wire from the distributor (car died as expected - tach still read 2000), disconnected the black wire (tach stopped registering change in engine speed as expected - still at 2000). I have not pulled the tach to see if there are any shorts on the circuit board, but that seems unlikely since it does advance with engine speed and drop a bit with power on. Anyone have a similar situation and possible solution?
P.S. Probably unrelated but I’d better mention...I replaced the stereo using the existing wiring just prior to this starting.
On a similar but different note...I was thinking of replacing all of my gauge clusters with digital displays. The ones I’ve seen so far claim to drive off of the existing connections, so I’m thinking this readout problem wouldn’t go away. Thoughts?

|UPDATED|6/5/2018 9:36:31 PM (AZT)|/UPDATED|

 It's possible that the gauge itself is out of whack. Then again, tach problems on these have normally been traced to either the filter or the circuit board. I would suspect the circuit board, before condemning the gauge itself. Unfortunately, the only way to check is to replace the board, unless you have a certified instrument repair place close to you.

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