Hey guys,

The tachometer on my '84 300D has not worked since I've owned the car. I never paid much attention since so many other things were broken, but now that a lot of the other things have been fixed it's time to take a peek at the lower priority issues, right?

I went to look at my tech amp yesterday, and realized my car does not seem to have one.

Where the tach amp should be is just an empty plug with a screw cap. It looks like this:


There is nothing underneath the cap, although some previous owner did stuff the cap full of paper?... Looking at the plug only pin 2 and 6 are active, and looking up a schematic pin 3 should be the tach signal, so I'm pretty convinced this '84 never had a tech amp.

I did a little bit of research and found that the cars that don't have a tach amp should have an Overvoltage Protection relay under the dash board that controls the tach and A/C.

So, I then went hunting for the OVP, which should be under the dashboard, behind the kick panel on the passenger side, right up where the passenger air vent is. It should look like this:



However, I don't have that either.


So, I guess I am either missing my tach amp or the OVP or does anyone have any idea what else could be going on?

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"The MB W123 is so bulletproof, you can drive them forever. Which is a good thing as it takes that long to get anywhere."
Betsie: 1984 W123 300D (hobby, 280k miles)
Myrla: 2001 Mazda Protege 2.0 ES 5spd (daily driver, 130k miles)
The Turd: 2007 Toyota Camry (wife's car, 118k miles)