Why is tail light dual filament?
 

I've been working out the gremlins in my rear lights.
I think I have it all cleaned up and working well now.

I replaced a few bulbs, cleaned the contacts with emery cloth, and added a touch of dielectric grease to the contacts.

I have one remaining question.
The outer most tail light has four contacts, presumably for dual filaments, the bulbs that are in there are dual filaments, but they only light up as tail lights (no brakes).
This corresponds to the labels in the bentley manual - only a tail light.

So why is it setup as a dual filament? Just wondering. Thanks

Also, in searching for replacement bulbs I found none, people have listed different numbers but none fit, the socket and bulbs have lock nubs that are not directly across from each other, but rather at a something more like a 10 and 2 o clock position if you are looking at the bulb from the bottom (or looking at the matching channels in the socket)
I'm sure I can get a replacement set from BMW with a new socket, but really?

http://farm9.staticflickr.com/8026/7...f679c6791e.jpg

After more research I believe I have found the answer!

In Europe the E36's came wired with "rear fog lights". When activated the outer taillight would glow brighter (ala 2nd filament) so that drivers in fog could see you better from behind.
This option was not available in the US and is not wired up through the harness. However the socket and bulb were still dual filament.

Here are a couple of sites I found detailing this.
The second is a write up to re-enable them, I have no desire to do so, but anything is possible.

http://www.dtmpower.net/forum/e36-3-...aillights.html

http://www.unofficialbmw.com/e36/ele...rear_fogs.html

Excellent find.

You are right. In Europe rear fogs are mandatory so rather then have two different sets of lights they just made them standard. The US cars have a few similarities between the Euro Spec ones.