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|I had my tach open a few months ago. It was an inductive pickup with a heavy duty wire for the primary. I do not think burning out the tach should be a problem. What you need to be concerned about is burning out the electronic ignition (or possibly some of the old, not so great, electrical connections). If it is designed to have a ballast resistor in the circuit, then you should have it. When the car is running, the impedance of the coil is much greater than the ballast resistance, so the extra resistance has very little effect. What it does is limit the amount of current flowing when the ignition is on but the car is not running so the impedance of the coil drops very low. Some electronic ignitions have this resistance built in, so additional resistance is not necessary. The manual for your pertronix should tell you.