I'm running LED bulbs. (Not the entire tail light assembly, just the bulb replacements). One of the issues with LEDs is that they draw much less power than the original incandescents. As a result, a wide range of problems have been reported, ranging from fast blinking signal lights, signal lights that stay steady-on instead of blinking, or lights that don't come on at all. As for me, my signal lights do a quick flash-flash-flash every time I start the car, and then everything goes back to normal. And the frustrating thing is that the symptoms vary from year to year. Some have used load equalizers with success. These are nothing more than resistors that are spliced into the facorty wiring to draw more power, which simulates the normal power draw of an incandescent bulb. They get very hot, so they must be mounted away from painted or plastic parts, and it can be difficult to know which wires to splice into. I bought some load resistors, but never used them. The flash-flash-flash doesn't bother me so much.

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"Si vis pacem, para bellum"
If you wish for peace, prepare for war

2001 325Ci (sold)
2003 Porsche 911 cab
2005 X5 4.4i
2006 English Bulldog