I’d check the voltage regulator. Had the fluctuating voltage while driving (Valeo), it got bad enough to drop under 8V and trigger engine failsafe- not fun.

Tried the new voltage regulator, been steady voltage ever since.

The brushes get worn and don’t make constant contact- hence the fluctuation.

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04 X5 4.8is | Sapphire Black + M Alcantara, 75K