99% sure it is in the cluster. M-B in their wisdom made the ground connections in their cluster go through mechanical connectors like screws and bolts when the cluster was assembled rather than wiring the sections together. An easy fix is to simply run a wire from the metal on the section of the cluster with the gauge to a known good ground in the dash (look for a grouping of brown wires all bundled up and connected to a big bolt on the chassis behind the cluster and that's a ground point) and see if that fixes it. Usually that will do it...you can't hurt anything by trying this. You're simply replacing a ground which has gone bad.

__________________
Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz