Originally Posted by Qurtyslyn
LED's will not dim unless there is another form of resistance (an incandescent light or resistor) inline with them. They are effectively On or Off.
That's not at all true. There are two ways you can dim lights and that's through added resistance or Pulse Width Modulation (PWM). Both methods work for both types of lights, it's just that with LEDs it takes a LARGE change in resistance to see a difference in brightness. Compared to incandescent where a very small change resistance is needed. PWM is better because it works the same for either type.
It is my understanding the newer TJs use PWM. Based on this thread it also sounds like there's no "hard off" and it's just turning the duty cycle down to 0, but there's some voltage leakage. Not noticeable with the relatively large resistance of an incandescent but noticeable with an LED.
The older TJs do not have this problem because 1) dimming doesn't really work with LEDs in the first place since it's resistive based and 2) it is a "hard off" switch.