The Compu-Fire electronic advance modules are used to convert the stock Dual Fire points type ignitions to Single Fire electronic ignition in 1970-1999 single cam Big Twin, as well as in Sportster 1971-2003. 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.