As stated above, here's the DIY link
LEDs have polarity issues, meaning they have a positive and negative side, unlike conventional bulbs, which don't care, hence why you only have a single bulb for turn indicators.
Here's the fix for that issue, it also fixes the all flashing issue when you install LEDs in all four turn signals.
http://faq.ninja250.org/wiki/My_LED_...t#Diode_method