Actually in the case of some vehicles the resistor ensure that the car's ECU correctly identifies that the LED is not a light which has gone out and is in fact active. I don't know how the Sienna does things, hence why I asked the question. If it's simply, plug and play, what kind of LED have folks used?Resistors are only needed for blinkers to prevent hyper blinking when switching to LEDs. I have LEDs in my highs with no issues. Then again, my highs aren't ran as DRLs. I have the LED strip at the bottom of my headlight.