You can spray "contact cleaner" on the rheostat wire and slide. You probably want it at max all the time, so solder across the pins does that or substitute a jumper wire for it. I put forward-shining LED bulbs which better direct light down the light tubes.

There is a tool to pull out the cluster, basically thin straps which hook the back. But, I remove the lower dash cover so I can push it out and also better direct the cables and unscrew the speedo cable for more access. Don't disconnect the oil pressure tube unless you must (mess, future leak), and surely never run the engine with it disconnected and open.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans