I installed a screamin' eagle ignition box on my '06. This ignition box is specifically for the '06, and the p/n is 32471-06. This is a plug and play box, with NO password learn procedure required. It took me less than 5 minutes to make the swap, fire the bike up, and ride away. No more detonation, and the speedometer reads correctly. If you do a Google search with just the part number, there will be a few dealerships from around the country who still have this ignition in stock. It is $119.95+ shipping/handling. Very happy with the results. This box retards the timing at full throttle to eliminate detonation, and raises the rev limit to 7000rpm.
Here are the mods that I did to my 06, and it rocked. These are simple mods, only requires about 2-3hours to do:
1. Vance & Hines straight shot slip-ons
3. Screamin Eagle High Flow aircleaner assembly.
4. Screamin Eagle Ignition Box, p/n 32471-06, as listed above. I ordered my box from Team Latus Harley in Oregon, via the internet, or you can call them.
I have recently traded out the Sportster for a 2009 Street Bob, but that 1200 was a blast to ride after these mods were done. No more detonation, sounded good, and hauled the mail.