This is really getting to me and would really like to solve this (Short of taking out the dash and installing all after market gauges in there).

At idles its not that bad, on far off by about 100-200 rpm normally, by the time is shows 8000rpm on my car's tach, the MS is only showing a bit over 7000rpm.

 

I think there is a tach adjustment screw on the instrument cluster. You would need to sync the dash tach to the Megasquirt, since the 'Squirt knows the true RPM and it is the dash tach that is wrong. But there will always be some variance.

 

I can take some of a couple hundred rpm, but about 1000 is not very nice to play around with at the track. Its either that, or i might have to actually get a shift light and be a bit of a ricer

But would an after market tach work better? I really considering changing that whole cluster anyways. My Oil pressure isn't working now neither, and no its not the sensor nor the wiring going to it. It wouldn't be too hard I think to make another one. No?

 

I don't think I've seen an accurate 1st gen tach in many years. My 83 is the other way around - indicates 7000 and it's actually north of 8000. If the temp is below 50F it doesn't work at all and then comes alive when it feels like it. I do have a loud piezo beeper running off the shift light output of the MS, this works very well for autocross. I set it for 500 before desired shift point and am happy.

 

So your rooting for me changing the whole dash then ?

 

Were it my car and it was as clean as your avatar seems to indicate I'd be inclined to adjust the tach first and try and get the stock stuff working properly. Disassembly, cleaning, reflowing of the solder joints behind the cluster, etc., would be a great idea while you're in there. Then if that was futile let the fabrication begin. IMHO.