If the speedo works but not the odo, he likely needs an odo gear.
If a W126 speedo doesn't work, he's got an electrical problem, either with the sending unit, the wiring, or in the instrument cluster.

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'79 300SD W116
'86 190E 2.3-16V W201
'92 300D 2.5 W124
'99 E320 4MATIC S210

I also noticed that one of the signal blinkers doesn't work so perhaps it's electrical... guess I won't know until I have a chance to pull it.

Thanks for the tips..

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MB 72 250 M130.923 114.011 170k The Beauty

sounds electrical to me. i drove my 84 300sd back to my dads house (2hrs away) to work on it when i had a bad alt, the battery was dead.. no electricity in the car at all. all gauges were dead. its all electrical on that car.

yes with that additional info check for a power issue to the cluster...you may get lucky with a quick free fix.

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

quick free fix...That'd be nice!

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MB 72 250 M130.923 114.011 170k The Beauty

we can always hope...

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

Depending on the size of your hand, you may be able to drop the lower panel and push the cluster out from the back with your hand.

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Adam Lumsden
(83) 300D
Vice-President of the MBCA International Stars Section

There's 3 ground screws and several clusters of ground wires accessible as soon as you take that cluster out. Check those!

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

I too have a problem with my speedo in my '84 300SD. It worked intermittently for a while and now it seems to have crapped out all together. I have checked all the grounds with an ohm meter and I am pretty sure ground is good. So the next question is how do I figure out if the problem is in the sending unit (at the transmission, right?) or the speedometer itself? And also, how do you disconnect the green wire from the back of the speedo (I assume from search results that is the hall effect sensor) but the wire seems to be in there pretty tight. Thanks in advance to anyone who can help!

lee

Lee

That single wire to the back of the speedometer does just pull straight off. It has a form of compression fitting that grabs the post that it pushes on. There are no threads on the post

You can solder a single wire across the two board connections where the dimmer attaches to the board. This will bypass the dimmer and give you full illumination on the dash lights

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'84 300D ~90k
'82 300SD ~171k
'82 240D ~175k
'96 Ram 2500 with 12V Cummins & 5 speed ~130k

Speedometer on a 126, since it is electronic, may also be a fuse. Don't ask me how I know.

I would definitely verify the fuses before pulling the dash apart.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Hey Ken and Sam - Many thanks - I will check it out and provide an update. Since it snowed in the nation's capitol last night I think I will wait til this weekend. lee

Well it was pretty easy to pull the cluster out just by grabbing the front of it and pulling.

Although I think I did more damage than good because now the hazard blikers don't work.

Other than that I tried jumping the dimmer and still now illumination. There were a few burnt bulbs so maybe that's the problem.

I forget to check the fuse for the speedometer so I'll have to look for that tommorrow.

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MB 72 250 M130.923 114.011 170k The Beauty

Ok well I'm still stuck with no speedometer and no dash lights. The odometer works.

Where would I find the sending unit for the speedometer?

Is it possible to test any of this stuff on a workbench?

I tried giving power to one of the multipin connectors on the back of the speedometer and in that case the dash lights work. I don't understand hwo the whole thing is wired since the actual power connection must go through the rheostat (which has been jumped) back intot he wiring harness and then to the back of the speedometer unit.

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MB 72 250 M130.923 114.011 170k The Beauty

The dash is actually very dimly illuminated... I jumped the rheostat so I can only hope that at maximum voltage it would be brighter than this???

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MB 72 250 M130.923 114.011 170k The Beauty