Tach needle bouncing

[Sklptrljay]

I installed a cluster I bought (year and a half ago--always takes longer than you think to get these things together), and It's giving me a few issues. Mostly I am concerned about the tach needle bouncing around. It's all over the place.

I grounded the cluster, I followed the HEI installation instructions (constant 12V instead of the resistance wire), It has a new pcb that's made in the USA ( I checked that the pcb had continuity internally).

I'm just stumped, so I was hoping someone has worked this out before. I'm wondering if it's just a bum tach? I didn't see a brand name on it.

Any thoughts?