I had a similar problem with the dash button lighting vs the gauges and after several full range turns of the dimmer back and forth and it cleared up.

Have not looked at it in detail, but others that I have seen is basically a carbon track with metal contact wipers on the knob. Over time, gunk can accumulate and create intermittent contact issues, especially on a part like this that rarely gets excercised.

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Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)