You might be looking at it the wrong way, maybe the problem occurs when the dash lites stop working. Maybe check a wiring diagram and see what's involved with the dash lites and work back from there, maybe not even a buss problem.
Or at least approach it that way

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)