my factory 1200 tacho works fine with my L20b with electronic dizzy, its a bit slower on the up take than the autometer though

My 1200 tacho also works fine with the management I'm using, which also controls the solenoid which supplies power to the positive of the coil. It only starts going haywire when it hits the limiter, which cuts the positive to the coil, it will then jumps back and forth between 7k and change and 0.

So yes, have a look at your connections again, it sounds like the behavior stems from a bad connection.

i have an after market tacho and i find it also jumps a bit. its not out of control but it sets the shift light off sometimes. maybe ill try the bad earth theory.

Ah alas, i have tried the bad earth thing, the wire loop is securly connected, so i ran a new earth to the "-" battery terminal, and no change, i then tried unpluging the earth, and still no change. I used a multimeter to check the ohms, i turn the meter onto the 200 ohm setting, and it said 124. Also i noticed when i turn the ignition to accessiories, but not crank the motor the needle hovers at 500 rpm. So what the hell am I to do? I cant figure it out, any more suggestions guys? Thanks