Brake light question
 

I had to change my brake light passenger rear again. Went to Oreill'ys. Now when he loked up on his computer it was a 2 filament lamp while the one that came off the car was one filament, I also checked the other side and it was 1 filament. Any idea what is the correct one.
In the manual it shows as rear lamp side/ marker lamp and brake lamp.
what is the difference between the 2.

thanks,
Dane.

What year is you X5?

On my 2001 4.4i the rear brake lights are modulated by the Lighting Control Module (LCM). The LCM puts about 3 volts to only ONE filament for the "running" lights; when the brakes are applied the LCM puts the full 12 volts to the ONE filament.

If a two filament bulb is installed the LCM would only modulate one filament of the two. It should work OK.

For the "Side/Rear light" feature the LKM puts out 3.8 V AC. The proper bulb is a double filament type. And, as withidl said, only one filament is used for both brake and side/rear lights. Complicated solution to a very simple problem.

I second what zulu95 said!

I think there's a method to their madness. By having the LCM control the bulb intensity by varying the voltage they can run one less wire in their circuitry to the bulb (the extra filament would require a separate circuit) thereby saving weight and assembly complexity.

its a 2004 model

It would have been sooo much easier to just run the wire! Their "solution" eliminates many cool mods or at least makes them much more difficult to achieve. Plus I'm sure the LKM would have been simplier and less prone to failure.