Question about 1984 Mercedes-Benz Mercedes Benz 300 Class

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Tachometer doesnt work

Tachomenter on my 1984 300D Turbo Diesel does not work. Thought it was the RPM sensor mounted on top of the flywheel housing so replaced it. Guess that wasnt it. Discovered that there was no continuity in one of the two wires between the plug in connection (to the RPM sensor) under the hood and the other end that puggs into the back of the Tachometer. Is there a switch or amplifyer, or some connection that could be out? if so where is it located?

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  • sqweet Jul 12, 2008

    I have the same problem in my '84 300sd

  • berndh Jul 16, 2008

    I have not received any reponse to my question. Am wondering what I'm doing wrong. How do I get an asnwer? Am I not looking in the right place

  • berndh Jul 18, 2008

    I signed up for the Premium Assistance Plan which states "Get timely email assistance from our Top Experts.
    Receive as many solutions as you need."
    I have not received any responses . . . Not a happy camper



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You can also poke around on places like eBay, or look in a junkyard for this part. Mercedes calls it a Tachometer Amplifier. Unfortunately, they are know weak points on these cars. I'd recommend resoldering the connections, but the internals of this part are potted in silicone, making it VERY hard to get at the electronic components inside. Your best bet is to just find a replacement for that part under the screw-on cap. My 1979 300SD has the same part with the same problem, alas.

Posted on May 31, 2009

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Hello, I can probably solve your problem but I don't know how I would get paid for it. I haven't seen this pop up under Premium Service on my end. Anyway, listen up. You probably have an earlier 1984 300D which has a TDC cap that controls the tach. It's located on the left fender apron about midway and has a screw-on black cap about 1 1/4" wide. If you unscrew it and pull up, it will come out and on the back side you should see about 3-5 pins This is the TDC cap and the most likely cause of the problem. Later 1984's and 1985 got the signal from the frt crank sensor.
If you find this information to be correct would you please enter a "fixya" rating.
Thanks, Gator241

Posted on Feb 12, 2009


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Posted on Jan 02, 2017

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2005_n405_newsletter.gif 2005_n105_newsletter.gif

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