Compu-Fire Ignition modules utilize the latest technology to provide the best ignition systems available for use on 1970-1999 Big Twin and 1971-2003 Sportster. Problems associated with other brand (early) electronic ignitions have been identified and eliminated. Compu-Fire ignitions are reliable, tunable and super efficient to provide years of trouble free High-Performance riding. Compu-Fire ignition systems eliminate the "Black Box" of the OEM and some aftermarket systems, opting to include all the necessary electronics into the nose-cone. For convenience and accuracy, a static timing-light is built-in! This simplifies installation and allows quick easy static timing. These modules work with the stock mechanical advance unit and have no rev-limiter for added performance under all riding conditions. Installation on 1980 and later models with OEM electronic ignition requires the separate purchase of a mechanical advance unit. Use with coils with a 2-3 Ohm primary resistance.