I'm trying to get a working tach on my 1983 300D non-turbo, manual transmission. I have all the parts, but don't know what the connections are for the tach plug. The plug I got off a '79 300SD has four wires: On the (+) side, a red/black and a blue/black. On the (-) side, a solid green and a green/yellow. The three wires on the output side of the tach amp (from same car) are: Brown-ground, one red/black, and one green/yellow.
Any help with the wiring would be much appreciated. Thanks.

I can speak only in general terms since I've had no direct experience. The brown wires are gound, of course, as you have said. The red/black/violet wires are +12V and the yellow/green wires are the signal that the tach electronics translates into RPM. The question that has to be answered is, is the stuff you got compatible with your car? How does a manual transmission, non-turbo 300D generate an engine RPM signal? There must be some kind of sensor on the crankshaft but if your car didn't have one to start with (you don't say that, I'm guessing) then you have to add something. Sorry to be so obtuse, maybe we can get someone with more experience to help.

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

There have been several discussions about this task, but focused on installing a tach on 240D's. You might try searching on that. Just for enlightenment, where is this plug that you mention, on the back of the cluster?

__________________
1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150

This the 240D thread on the tach you were thinking about?

DIY tach for 240D w EGR- easy!


Charlie


sent from my pos computer

__________________
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 for the responses.
First, there is a bracket on the front of the engine to hold a sensor, and a 'tooth' on the harmonic balancer. I've bought a sensor which fits the bracket and has a plug that is compatible with the tach amp I got off a parts car. The tach is part of the instrument cluster that a previous owner installed.
Second, yes, the 4-wire plug that I'm asking about plugs into the back of the tach, on the two posts as seen in photo #2 of funola's 8-27-07 post: DIY tach for 240D w ERG.
Third, thanks for the link, Charlie. My car is a Euro model, so may not have an EGR...I'll look.
Fourth, my current thinking on the plug wiring is this: red/black on plug goes to +12V; blue/black is not needed since it appears to have supplied +12v to the "worn brake pad" light on the instrument cluster; green/yellow carries the signal from the tach amp; solid green goes to ground (?)
Let me know what you think.
Cheers

My DIY tach for 240D w EGR is different than what you are doing since you do not have a EGR controller. Since your parts are from a 79 SD and the wire colors are different than wires from a W123 diesel tach amp socket, which has 3 solid color wires (brown gnd, black +12, green tach out signal to tach in cluster), you'll have to find a diagram from a 79 SD and figure it out.

Maybe this diagram will help with the pinout.

__________________
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

Yeah, you'll need the amp and a proper tach gauge, old style two prong, with the proper wiring harness.

Attached Thumbnails

   

__________________
83 SD

84 CD

Yes, the amp, plugs, and tach gauge all look like what I have collected. Now I just have to figure out the wiring of the tach gauge plug that I got from a '79 300SD. The plug has four wires: A red/black and a blue/black going to the (+) side of the plug, and a green/yellow and a solid green going to the (-) side of the plug. My current thinking is that the red/black carries +12v to the tach gauge and the blue/black is not needed because it appears to have carried +12v to an instrument light that is already supplied with +12v from another source. I assume the green/yellow carries the signal from the tach amp. My only remaining questions is, where does the solid green go? I guess I should post this question for someone who has a wiring diagram for a '79 300SD. Should I start a new post for this question? Thanks

Here is a link to the W116 FSM:
Mercedes-Benz Model 116

Click on the "Wiring Diagram" button and it will download/open the diagrams.

On PDF Page 9 you'll find the tachometer gauge in the cluster.
On PDF Page 8 you'll find the TDC Sensor Adapter wiring (plug that goes on the fender)


I snipped out the TDC Sensor Adapter wiring:

You'll need to connect:

Black to the sensor on the balancer
Violet to the sensor on the balance.

Red to 12V Power
(something) to Ground (they didnt list the color)

Green/Yellow or Green/Black to the Tachometer Gauge D+ input.





For the Gauge

It has two connections. One is to 12V power. The other is to the Green/Yellow or Green/Black lines coming from the TDC Sensor Adapter wiring.
Ground is achieved by contacting the metal plate of the gauge to the speedometer unit. There is a grounding strip on it that provides ground to the left/right gauge pods.

Hope this helps!

__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

^ Thanks for the link.

__________________
83 SD

84 CD