On my e53 I rewired the lamp so both lights used both filaments and had all four act as run and brake.

On the newer BMW the LCM will adjust the light usage to compensate for burned out lamps so that might be a possibility especially if you attempted to use led lamp which will not dim as meant to be.

With four new lamps they should be similar in brightness but the lower using the low filament and the top dining the high filament.

Something might be wired wrong or bulb model wrong etc.

No light should be bright in the "on" position only the bottom two should be bright when braking.

You can measure the voltage across each lamp in run and brake to root out where the problem is

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)