It could be the voltage regulator going bad. Sometimes the regulator problem can be intermittent.

However, since you can tie the problem to replacing the brake light I would continue to trouble shoot there. Be sure your replacement is the correct bulb and be sure that the contacts in the bulb socket are not corroded. Corroded socket can cause a brake or stoplight to go on and off. If you checked the bulbs the first time and they were not out that is a good sign of corrosion. Sometimes all you need to do is apply dilelectric grease, sometimes called electrical grease or bulb grease to correct the corrosion.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas