Tail light bulb question
 

Hi all.....looking for an answer. I noticed today while changing a rear bulb that on the tail lights...the upper of the two bulbs is a dual filament bulb, however, I have only seen it light up as a tail light bulb. So....why the dual filament..? Hope this makes sense...just bugged by it and looking for an answer....

It is also a brake light. Check to make sure the bulb is correctly seated in the socket. Check the other side to confirm that there are two bulbs lit for the brake.

well....when you look at the tail light, there are two bulbs that come on when you turn on the head lights. When I put my foot on the brake, the bottom of the two bulbs gets brighter. The top bulb does not change, however, that is the one that has the dual filaments..? (hope that makes sense)....

I just went out to my car to check it out. Your right, two filiments for the top red bulb but only the bottom bulb is the brake light. Therefore, I'm wrong when I said that both bulbs were for the brake and I don't know the answer as to why there are two filiments on the top bulb.

Probably for Europe and fog lights or something...I remember a very similar thing on my E36...

I belive it is for adaptive braking. When you apply pedal hard or ABS is active the it should also light up as well as the regular brake lights. Gives the person behind you a BIGGER warning.

This makes sense

I was wondering about the adaptive brake light thing, but I did not know if that is something that my X5 has...does anyone know..?

I think it is on all X5s, check your manual or the pdf version on this site, around p. 98 or 99. It describes the adaptive brake feature and it is not listed with an * which would indicate optional equipment.

You could always just hang a big mirror on a wall and back-up real fast into it applying the brakes to see if the other lights come on. Just kidding.

Seriously though it looks like it is standard equipment on all models of the X5.