I just bought an 84 300sd from the 84 year old original owner. Always garaged, dealer maintained, seat covers since new, new tires & ac compressor.
Not a single spec of rust, it's as perfect underneath as it is on top. I didn't haggle, he was asking $4500. Everything works, dash clock, right mirror, cruise control, sunroof, all a big improvement from my kinda clapped out 300se.
The only thing that doesn't work is anything in the dash light circuit, nothing for climate control section or speedo cluster. Turning the dimmer knob does nothing.
I have no problem digging into this, I just wondered if anyone had a simple answer based on experience.
Thanks

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85 300SD. 88 300SE. 85 560SL.

Perhaps you tried already, try turning the dimmer knob repeatedly as in a lot. It may have a dirty contact.

Good luck with the new ride, sounds nice!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Standard troubleshooting......first and foremost, check the fuse(s). Then pull the instrument cluster and check for power to the lighting circuit at the big round connector (Not sure which pin it is but I am sure others will chime in) if no power there you have a wiring issue. If power is present, most likely it is the dimmer rheostat. Also, while you are in there, replace the dash bulbs!

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

Remove the gauge binnacle and invert it ~ find the dash lights rheostat, identify the two copper strips and solder a short bit of wire across the two rivets, re assemble and Robert's your Fathers Brother .

Cleaning these rheostats sometimes works for a while but they're typically dead and the dash lights are so dim you'll appreciate the brighter light once the old dimmer is by passed .

Whilst the binnacle is out and in your lap, take the time to gently remove each bulb and wipe it clean with a clean dry cloth or toilet paper, you'll be amazed at the thin coating of dust on each bulb, it really does hinder the Lumens from getting where they need to go .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Thank you

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85 300SD. 88 300SE. 85 560SL.

Welcome .

The collective brain trust and experience here is staggering .

I'm a Journeyman German car Mechanic yet I only dipped into Mercedes 20 years ago and the fine folks here have been endlessly helpful .

These are not overly complicated cars when viewed against modern cars but they -do- require patience so don't hesitate to back off and let things simmer when you get stuck or frustrated .

Like all German cars, even when they're in tip top shape they need constant touching .

Most used Mercedes have multiple things that need attention then they're like new and ready for the long haul .

Don't be in a hurry to throw parts, these cars are designed to be incredibly adjustable .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Jealous!

Pull the kick panel and see if there is a rheostat like the w123 cars use. I don’t recall if w126 of that age have them. On the w123 you can unscrew with a right angle driver without even messing with the cluster. Jumper the rheostat and see if that helps.

Disconnect battery when messing around the cluster. Very easy to burn up a trace somewhere.

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)