The Compu-Fire electronic advance modules are used to convert the stock Dual Fire points type ignitions to Single Fire electronic ignition in 1970 thru 1999 single cam Big Twins, as well as in Sportsters from 1971 thru 2003. They may also replace the Prestolite type modules and H-D electronic advance modules. They have a built-in, non-tunable advance curve that works great on stock and mildly tuned engines with stock compression ratio. Ignition comes complete with a trigger rotor that replaces the stock mechanical advance unit. Use with 2.5 thru 3 Ohm Single Fire coil.