The Overvoltage protection relay has one or two fuses on it which will cause the tach to go dead and a bunch of other stuff not to work.

Its behind the battery, it will be a tall silver relay with a door on top.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)