Screaming Eagle 32654-98 switchable ignition - 4 curves, adjustable rev limiter, single fire capability and fixed ignition retard for Nitrous (should you feel the need for speed). Same as Dynatek 2000HD. No longer available from HD, but over £200 when it was. Two small cracks (repaired) on mounting holes as a result of a few years use on poorly produced S1 frame. Fits M2 (up to 2000), S1 and S3 (up to 1999) - if you have the same plug, it fits your bike. Also fits lots of Harley Sportsters etc.
£100 to you.