My take on the dual filament one used is for part number simplicity. Also in a way a built in spare.
If the brake light goes out you can switch with a run light which has an unused brake filament. I found it very odd myself and the answer I came to is purely speculation.
I was very surprised to find out the front corner lights don't use the low filament of the dual filament bulb for either run/park/corner or for the dim parking mode. I tried some led in the front and had to go back to Incan.
I left the back turn signal LED though and they are stunning bright. Make no mistake when I've got a signal on from the back.
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2011 E70 • N55 (me)
2012 E70 • N63 (wife)
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