tachometer

[fresh water]

tachometer on my 1980 323 pearson suddenly became highly in-accurate. Needle moves and bounces. tachometer works off alternator.
This is a repost because I could not locate original post. Operator error

[Bill O]

Check your tach wire end at the alt. and clean if needed. Wire maybe loose on tach side. Inspect wire between for breaks. Also check/adjust belt tightness.
If still bouncing around, may have an issue w/the alt. Did anyone recently turn off the key or switch the battery selector w/the motor running? If so, could have blown a diode. Would check alt. output or take it to an alt. repair shop to have it checked.