Also they are not very bright to begin with so your rheostat may be fine. The optic prisms are extremely inefficient and waste a lot of light. I've replaced my bulbs with LEDs....it took 6 Ultra-high-intensity LEDs on each side just to make the gauges visible at night. Bulbs were nearly unilluminated.
All I have heard is the rheostat completely failing, making the entire gauge cluster and center console fail to illuminate. Although since it is often the springs failing inside, I suppose it could easily get stuck on half-dim. The rheostat is very easy to jump, solder a wire in between the only two soldered joints on the instrument cluster board behind the unit.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth