Tach accuracy question

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I too "suffer" from this SW tach issue which I and the previous owner called "Float" or "Bobble". In my case, this symptom seems to be a "feature" only when the engine is COLD. The darn thing just flips from 1K to 2K higher, usually never lower RPMs.

When the engine warms up it settles down to read right but is still very sensitive and not "buffered" it appears.

I have the UniLite Malloy distributior.
Mallory Power Conditioner.
Ballast Resistor
Mallory Pro Coil.
MSD 6AL ignition box

One thing I do not have is that tach Adaptor. This is the second 6AL box I have been running. The sympton was the same with each so I think we can deduce it is not a feature of a specific 6A box.

I wonder if there is some sort of inductance caused by cross talk of wires. My electrical training (Ham Radio) tells me that voltages can transfer from one wire to another if they are in very close proximity to each other. Ususally, this can be cured by separating the wires or coiling the wires or by the use of Ferrite Cores (little magnets at the end of each wire, you see these alot on Video Cables from you Monitor to the PC).

Does anyone know the part number of this Tach Adaptor? Is it an MSD part or an Mallory Part?

All Ears Here... Cheers