Some ppl may experience the problem after they replaced their original turn signals with LED turn signals,  the LED turn signals either flash too fast or they don't blick at all, they just stay on constantly.

The reason is the stock mechanical flasher unit needs a specific current draw from the lights in order to work properly. If your LED  don't draw enough current, then your flasher will blink too fast. You can fix this problem by adding parallel resistors to the circuit.

Usually a 10ohm 10v resistor from radio shark (#271-132) could fix the problem, if you are only planning to install either front or rear LED turn signals; If you replace all four turn signals with LEDs, the fix for the problem could be more complicated.