I recently changed out the rear turn signals with LED ones, as we lost a lens. So to accomplish that, you have to replace the stock flasher with an electronic one. I used the LFS-1-FLAT electronic flasher recommended by spud located here:
http://www.superbrightleds.com/flashers.htm
By testing with a meter i determined the wiring which is shown in the following picture:
Here is the rear of the bike with the LED turn signals I bought off
ebay. They are brighter than the stock ones and flash at the correct speed.
Dave