1980 300SD w116 model.

I've tried 3 different tachs and 2 different sending units on this one. All of those parts functioned in other cars. The tachometer registers at idle (not accurate, though), maybe 200 to 300 rpm. Higher than idle it drops to zero.

At idle, turning a turn signal on causes the tach to jump up and down.

I get volts at the back of the instrument cluster: 12 to 14 or so, but tach dosen't register above idle.

Everything else works on the cluster.

Anyone run across this on before?

Any ideas?

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Rev. Dr. G. Church of the SubGenius
It doesn't take a genius

Have you looked at the tach sensor on the flywheel? I believe this holds true on the '80 -

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BENZ THERE DONE THAThttp://www.peachparts.com/shopforum/...c/progress.gif
15 VW Passat TDI
00 E420
98 E300 DT
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97 S500
97 E300D
86 Holden Jackaroo Turbo D
86 300SDL
(o\|/o)

Try grounding the instrument cluster to the body, it sounds like you may have a bad ground because the turn signals are affecting the tach.

Pardon the question, but you mean just run a wire from the metal back of the cluster to bare metal on the body?

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Rev. Dr. G. Church of the SubGenius
It doesn't take a genius

more or less. I think Craig is on the right track with the grounding suggestion. Next time my cluster is out that *#@ tach is getting a serious ground wire soldered to it's a*&!!

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

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

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

GDEMOSS01....Just curious, inquiring minds want to know and all that jazz, does your cruise control unit work?

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Mark
1983 300TD Wagon
Even a broken watch is right twice a day

Yes, my 240D instruments were acting strange, so I just ran a wire from one of the mounting screws on the instrument cluster (connected to the metal frame of the tach/clock or speedo) to one of the ground points under the dash (a bolt with a bunch of brown wires connected to it). In my case the problem went away, I must have had a broken ground wire someplace.