Hey guys - recently my 5 year old OER tach started reading wrong (no changes made to car). It always worked well with the MSD 6AL box. Changed to MSD Digital 6 box 2 years ago, still worked fine. Lately, it's been reading high at idle (reads 1200 when really 950), and after idle reads low (reads 1600 when really 2000).
Already checked ground, tried new ground, still same. Haven't tried anything else.
Any of these symptoms ring a bell? Not sure where to go next.
Thanks.............................DC

If you search the archives you'll find lots of threads on tachs misbehaving. They are very finiky depending on the ignition system you're using. Check the electrical forum stickies - I believe Jim M. posted a schematic for a tach filter that is quite common. Recently someone had luck installing the filter and a diode. Unfortunately you'll have to cut and try - there is no definitive fix. Hoepfully the filter (and perhaps a diode) will fix your problem.