Factory Formula S Tachometer question

I have a 66 Barracuda 273/auto with a Fourmula S Factory tach that was rebuilt still in the post office box when i bought the car it came with the wiring diagram hand written by the re-builder . I wired it per the diagram and it works however the needle floats at throttle it's not jerky moves it just swings 500-800 rpms . The in cluster gauge looks correct but the circuit board is mounted in a square plastic box i have under the dash not like the round type in the kick panel , What could be...

Read more
Author: lou3500