kz1000p electric tachometer issue

For Christmas my mom got me a kz1000 police gauge cluster (wow!) and I swapped over them onto my kz1000 csr but I've been having issues with the electric tachometer. 

When i turn on the ignition the tach will sometimes bounce a little from 0 and works pretty well until about 4k rpm. Above that, it starts bouncing all over like it has a loose connection or something.

I thought it was the splice into the black wire so I redid it and checked if there was any resistance in the wire; there was none. I also resoldered some of the parts on the circuit boards in case there was a broken joint.

I did not test the coils to see if that made a difference. I cant find any way to find the issue so here I am!

the electronic units have components that do not age well. Specifically, the electrolytic capacitors. They contribute to smoothing the ripple/noise in the ignition system. I replaced these capacitors in mine, and have had no issue.