Courtesy of SUPERBRIGHTLEDS.COM:
"Turn signal issues with LED bulbs
LED brake/tail lamps will not flash with thermal flasher units due to their extremely low current draw. Also, with stock flasher units, the turn signals may flash faster than normal (Hyper-Flash). These installations will require an electronic flasher unit, available in our car bulb shopping category (for some vehicles) or at your auto parts store. Try to find flashers designed to work with LED bulbs, they will say "LED compatible". Often HEAVY DUTY flashers will also work with LED bulbs.
We offer some LED Flashers in our Tail/Brake Turn Signal Bulb category but we do not know which one (if any) will fit your vehicle. You will have to compare the pin-out of your flasher with the pin-outs of the flashers we offer, to see if we have a match, BEFORE you order one. Sorry but we do not have a flasher application list or the expertise to tell you which of our flashers will fit your vehicle.
Another fix is the installation of Load Resistors which are wired across (in parallel with) the turn signal bulbs to simulate the load of a standard filament bulb. We also have these available in our car bulb shopping category."
BULB Identifier:
http://www.sylvania.com/ConsumerProducts/AutomotiveLighting/LampReplacementGuide/