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

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.

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.

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

I'd go with bad earth too. Had the same issue once. Suggest running a length of wire from the tacho earth wire direct to the negative battery pole and see what it does then as another way to check.

electric dizzy should not make a difference. It sounds like a bad earth. ensure your eart connection is less than 1 ohm.

hmm okay, im not sure what dissy i have, it was whatever is on the motor. Any suggestions for a after market tacho that would fit in that sqaure hole in the 120y dash?

i had the same issue when trying to run a factory 1200 coupe tacho with my 12a engine (electronic distributor). it jumped about all over the place.

im with dd on this, it may be the problem if you have an electronic distributor in the l20b. do you?

my fix was going aftermarket.

nah its another old one...

That one that wraps around the screw is the earth I think, I am sure dd will correct me otherwise.

I could be that the PCB has dry joints. Is the tacho a new new one, or a new old one??