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For Evolution® and Shovelhead® applications, ballast resistance is used to limit coil current. In these systems, the resistance of the coil primary windings serves as the ballast resistor. Primary resistance is typically 3 ohms. Newer Twin Cam 88® applications use a coil with very low (about .5 ohm) primary resistance. Coil current is limited electronically within the module by restricting the charging time.