Speedhut tach

[Boony405hp]

i have a Speedhut electronic tach for my 5.7 swap. I've set the pulses/cycle but the needle still has the occasional jumpiness and flicks about waywardly. I've heard of resistors being installed on autometer gauges for noise cancelling but not sure about these? I have run the cable seperate from other cables to avoid noise, I even tried one with a shielded sheath. Anyone else run this setup and have some tips? I tried cutting the purple wire but that just stopped the gauge reading at all.

Thanks, Dave