AFtermarket Tach

[LethalEthan]

I'd only keep it if its needed to run the coil. I didnt have any sound problems when I switched my coils out.

[camoit]

The ballast resistor lowers the voltage and wattage draw at an idle when the coil has more time to charge between sparks. (IE: points closed) At a higher RPM it allows the voltage to increase since the coil needs more power to charge to full power with the shorter time between sparks. When the distributor opens the circuit (IE: points open) the magnetic fiend around the coil core is allowed to collapse into the coil and the voltage is increased to a High voltage state. Normally in the (KV) Kilovolt range. That power must go some where so it runs up the coil wire looking for an easy path to ground. A Tachometer needs to connect to the negative side of the coil. As this is how it tells how many times sparks. New electronic ignition system can cause the tac not to work correctly because the grounding of the coil may not be a complete and true ground. If it has to much Resistance in the circuit the tac may be unsure if the ground is made and give you incorrect readings. Some tac manufactures require a special adapter that can read the signal the coil is receiving.
I hope this helps.