I would like to add a Tachometer to my 1980 W123 300D. I would like to use the Instrument cluster Tachometer, but these are extremely rare in West Oz (West Australia).
What items are needed to obtain the signal for the tacho from the engine (sender unit?) and are any other items required to make it work, other than the Sender unit and Inst Panel?

Lastly, would anyone be able to source these for me (metric Speedo please) and send them to me in Oz?

Your assistance is appreciated.

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Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.

Just got done doing this on my car. You will need the tachometer guage that goes in the instrument cluster, the RPM sensor (not really a sensor, but a signal "amplifier") that bolts to the fender well, and the reference (top dead center) sensor that bolts to the engine. The tach and sensor wire into the RPM sensor. You will most likely need to find the harness connector for the RPM sensor out of a junked car, as it is part of the wiring harness and a special plug. The connector on the guage could easily be fabricated (standard MB pins).

According the info I found, engines with serial number 912 12 076009 and newer are set up for the reference sensor. If it is earlier, then you will most likely need to buy the reference sensor mount (small rectangular plate with a hole and stud), the timing pointer bracket (which bolts to the engine and the reference sensor mount bolts to), and a crankshaft damper (which has the pin sticking out of the side that the sensor looks for). But you will need to check your car to see if these three items are present. The mount is located under the vacuum pump and you can see it from overhead, and you should be able to see the pin sticking out somewhere on the circumference of the damper if present.

If you have the parts, it is an easy do-it-yourself project. Get a wiring diagram from a 1982 or newer W123 300D and your set.

The RPM sensor and reference sensor, and I would guess the damper, are available from pretty much any Mercedes parts dealer. The rest may require going to a junkyard or the official Mercedes-Benz dealer. When getting the electronic parts, get them for a 1982 to 1985 300D. For the hardware, get them for a late 1980 to 1981 300D. I think the timing pointer and damper are different for the turbos.

When installing the reference sensor, make sure there is a small gap between the damper pin and the sensor. That's a quick way to destroy a sensor if they make contact.