I used LEDs in my tail lights and rear signal for a while years ago. They are not visible during the daytime... sorry.

Vividkid82 is exactly right. The LEDs require less power to create light so your flasher thinks that one of your bulbs is out because not as much power is being run through it so it cools faster and flashes faster.

You can add resistors or you can get another flasher with a lower resistance.

honestly, you may think that they look cool, but they're unsafe and really aren't worth paying to have your car fixed cause someone didn't see that you were turning. Your ins company won't pay to have your car fixed if the police report says "altered factory lighting". h:

hih