I have a 1983 240d and i wanted to add a tach. so i looked around at some guides and im stuck. i got some parts off a 1985 300d turbo, like the sensor at the crank and the black round thing with the cap and the tach, but i dont understand where to hook the cables.

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1974 240d
1983 240d -sold
1989 420sel with om606
1994 s350 turbodiesel - sold

85 has no tach amp. The black round thing in 85s is just an empty socket. Get a black thing from a pre-85/mid-84 and maybe also get another tach to go with it (the pins are different but it might still be usable).

Or, a totally different technique, hooking into the pickup that's already there:
DIY tach for 240D w EGR- easy!

The 85 tach has different connections on the tachometer itself, as it gets a signal from an intermediate computer.

The 85 still has the pickup for the hall effect sensor, so that a mechanic can run a separate tach from there.

Youll need a true tach amplifier (might as well buy new, most older ones can be flaky) and a tach from an older w123.

I did this the opposite way - to get a working tach on an 85 300D that had an older engine swapped in and had all messed up electrical parts. Worked perfect.

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

I put a tach in my 83 240D using the EGR computer as the tach amp. Search for my post. There should be some info there that may help you in wiring up your tach amp and how to power it from your cluster. My 240D is now a parts car and I have sold the tach setup to a member here and he is enjoying it in his 240D.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

If you can get the appropriate parts from a donor car, you can hook one up. If you use the egr set up, you'll need a later tach unit, one with a three prong plug. If you use the (early) set up, you'll need a two prong plug tach, a wiring harness and an amp.

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83 SD

84 CD

So i tryed funola's egr thing and its not working out for me and was wondering if its because i have an 85 tach with the 3 prong in back. or because i was misssing a ground because i soldered the 12v part in back and did the red and black wire pair and put that in.

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1974 240d
1983 240d -sold
1989 420sel with om606
1994 s350 turbodiesel - sold

I've been through the same thing with the 3 prong tach and can't figure out a way to make it work. You'll need a 2 prong tach.

It seems that the 3 prong tach uses a pick-up from the transmission. I grabbed a sensor from the PNP but our trannys don't have the necessary mounting location.

I've leads connected from the EGR computer and all ready for the 2-prong one... now I just have to find it.

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'83 240D

I am not familiar with the 85 tach. What's the difference between the 3 prong and 2 prong tachs? The soldering I did was to provide switched power to the EGR computer/tach which I doctored up. You can do a little trouble shooting with a DVM. Check that you have 12V power and ground to the tach amp and the tach. If not, fix that first. Then put the DVM on low ac scale and measure the output of the tach amp with engine idling. You should see a voltage there (maybe about 100 mv). If you rev the engine, the voltage should go up. If it goes up, that's an idication the pickup and tach amp is working. Now you want to check that the tach amp output is getting to the tach so check for the output from the tach amp at the tach, you should see the same there. If you have signal at the tach and it has power and it is not burned out it should work.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

The 84's and 85's used a tach with three prongs and took the signal from the transmission.
But if a two pronger works with the egr set up, good, as there are more available.
I only have those to take a pic of.
Is the egr thing a Cali deal? I don't have an egr computer or ecu.

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83 SD

84 CD

Pretty sure I mentioned before that 85 parts don't work. 240s should still have the pickup off the hb. Very easy to install- 2 wires, an amp and a non-85 tach...

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

Well the tach has two wires, but the wiring harness has three, somewhere here is a description of where the other wire goes, but I think it's a power source.
A pic is here,
240D tach

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83 SD

84 CD

The 84 & 85`s get their tach signal off the flywheel, not the transmission.
the sensor fits into the adaptor plate between the trans and engine.

The signal does then go through the black box behind the passenger kick panel.


Charlie

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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

^ Thanks.

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83 SD

84 CD