I just did this splice fix and it worked perfectly on my 85. Posting in case someone else has my symptoms.....
My tach worked through about half of the throttle range. Where it operated it was fine, but through about half the pedal travel it would drop to idle speed and a loud clicking would come from the rack position sensor on the injection pump.
The clicking was loud enough to be heard in the car and loud enough to make folks on the sidewalk look as I drove by.
The EGR connector was full of water from a new windshield leak I now know I have and must have been shorting across to the rack position sensor.

To the previous poster, I am not sure the transmission has much electrical control beyond the kickdown switch behind the throttle pedal. I would suspect something going on in that circuit.
I think the kickdown switch circuit uses signal from the tach so if it is stuck closed or otherwise malfunctioning, it would cause the transmission to hold first gear like that because it thinks you are holding the throttle to the floor. Without tach signal its not working at all and shifting normally.

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1985 300 TD 448K
1984 300 TD 278K

1983 240D euro 240k
1994 f-250 idi turbo 330K
1986 f-350 IDI
1987 F-350 IDI

1985 JD 1050 4wd
1965 IH 3660

The leak into your EGR controller is not from the windshield! It is from the opening(s) of one (or both) of the 2 wiring harness's outer shield in the engine bay. One is under the battery tray, the other is a connector middle of the firewall.

Per this diagram, the EGR controller has no connections to the transmission or kickdown switch. Maybe there are other diagrams that does?

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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

Good find. Swapping a 83 motor into my 85 3000sd and I belive troubles ahead!

The engine should not have anything to do with it.
Swap the adapter plate off the 85 engine, and bolt it
onto the 83 engine. Then plug in the sensor wire to
the adapter plate.

Iam assuming the SD is the same as the 85 300D, as
far as I know it is the same.


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

Yeah well I discovered the intermediate plate difference after bolting up my flywheel clutch and trans to the 83 motor. DOH!!! I assumed the front sensor ran the tach on all of them. I just don't know if the tach will still work without the IP sensor wire hooked up and all that emissions bul Zip taking up room on my floor. Being that I wasted a day swapping that plate and trying get unsuccessfully to get the hex plug out of the water jacket for the second temp sensor I sure hope it works. My first turbo manual swap afyer years of wanying to, living without a tach would really annoy me.

Having read this entire thread, I still have a question. (My tach has stopped working, after working intermittently for a year or so.)

A: First post said to splice white (20) to grn/blk (25). (and plug back in??)

B: Later post says to jumper 20&25 as well as 16 &14 (and presumably tape up and leave unplugged)

I have no EGR, A/C doesn't work, 85 Turbo. What is the difference and which is preferable.

Or could this be OVP or it's fuse? I read that fuse is up under passenger dash. Is there a relay there as well. If I jumper the wire to tach, are the fuse and OVP required? (I obviously need to read up on this stuff )

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

I did like post 21 by funola. I removed the EGR Box since all the vac parts were suspect and thus removed. My problem was the OVP Relay (not it's fuse atop), which is only used for the EGR Box. Those are expensive to replace, so I just tossed it and the box. For those readers jumping in here, if your tach stops working in a 1985, you will lose AC since the Klima relay requires that signal. It routes thru the EGR Box. I think 1984 is the same re fixing the dash tach, though doesn't have Klima for AC.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Old thread, but there should have been a correction to this. I think Funolo mentioned it later in thread. Maybe it doesn't matter but the wiring pictures show 20-25 correctly as per the text, but the other jumper in pictures goes from 14 to 18 instead of 14 to 16 as per the text.

Seeing 20-25 worked in post 1, perhaps that jumper is all that was needed? I tried that but it did not work. So I added the 14-16 jumper and the tach came to life!

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Not sure what pin 18 to the “trimmer plug” does. From the two wiring diagrams one lead from the rpm sensor goes to 16 which should logically connect to something…otherwise you have effectively disconnected your magnetic pickup. Doesn’t make sense, but hey if it works on your car, go for it.

The above photos sure look like 14-18.

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

That is exactly what I was saying.

The pictures don't match the text of the posts and are likely wrong.

20-25 and 14-16 is what I used. And this worked.

Graham

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5