No resistor required on my vehicles.

Cars that have warning lights for burned out bulbs usually require some sort of resistor. If the car doesn't see enough of a current draw it will give you the warning. LEDs draw very little current and will set off those warnings.
Old school thermal flashers (used in all older American cars) will not work properly with LEDs as turn signals. The fix is a cheapie electronic flashed. You're right back to plug and play.