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Old 11-12-2012, 09:51 AM
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Posts: 59
1984 300D Tachometer?

Can anyone tell me how the tachometer on a 84 300D gets its signal? I know the 84+ cars had a different system than the 83 & previous cars. I unscrewed the black round tach sender on the fender well, but there is nothing under the cap. Likewise the same on my 84 300SD, but the tachometer works perfectly on it. Also, is there an in-line fuse for it. The fuse in the fuse box has been replaced.


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Old 11-12-2012, 10:23 AM
toomany MBZ's Avatar
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Join Date: Nov 2006
Location: central Va
Posts: 7,820
There is a fuse on OVP relay located rear the glove box.

The last shot is courtesy of someone else, I think the 84's and 85's were placed slightly differently.
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1984 300D Tachometer?-screen-shot-2012-11-12-10.21.32-am.jpg   1984 300D Tachometer?-screen-shot-2012-11-12-10.21.43-am.jpg   1984 300D Tachometer?-screen-shot-2012-11-12-10.22.14-am.jpg  
83 SD

84 CD
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Old 11-12-2012, 10:55 AM
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Join Date: May 2007
Location: Out in the Boonies of Hot, Dry, Dusty, Windy Nevada
Posts: 9,585
The 84/85 pick up the tach signal from the adaptor plate between the engine and transmission.

Look down below the oil filter housing, and you will see a black sensor bolted to the side of the plate. a black cable runs up across the firewall towards the passenger side. there is a flat plug on the firewall where the cable plugs into. this cable then goes to the "Black Box" behind the pass side kick panel.

This black box controls the EGR, but takes in several signals from various places. including one from the metal box on the back side of the IP. that is the Rack Position Sensor.

I have had my 85 since 97, and it has never given me any problems. I even swapped in a 4 spd and use the 240D FW and the tach still works. so it isn`t dependant on the automatic FW for a signal.

I think the OVP relay on the sedans is up under/behind the glove box. never given me any problems, so haven`t looked for it.

The SD might be behind the false firewall under the hood. not sure, but have seen some in that area in the PNP`s.


there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works
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