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  #1  
Old 05-15-2019, 04:35 AM
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W123 tach

G'day all, well I got myself a 2 pin diesel tach from the USA, i also got a tach amp

the engine i got is om617A and it has the pickup on the front of the engine

the pickup wire is installed, the tach amp is in place

I'm just having trouble wiring it.


I tried following this guide. ( see attached picture )


i used a multimeter to see which wire was which, the green + yellow wire is number 3, however i'm struggling to find where it's supposed to go in the wiring loom

I can't find the correstonpding enf to connect it to.

the car has the tach plug behind the instument cluster, but for the life of me i can't find the other end, i tried tracing it, but it goes into a 2 inch thick loom of so many wires under the dashboard and from there i lose it :/

with the connecting wire behind the dash
I see the + is for straight 12v( black + red stripe ) , and the other straight black ) is for signal. But no luck, i tried running a wire straight from the number 3 output from the tach amp to it, and no go :'(

the car

1985 280CE ( manufactured in 1985 ) with om617A engine transplanted into it. I'll grab some pictures


off of the tach amp i have these wires.

+ 1 more for power.

i have

1x brown = ground
1x red = +12V ?
1x black + red = unknown
1x green = unknown
1x green + yellow = signal to tach.
Attached Thumbnails
W123 tach-tachamp.jpg   W123 tach-60346402_347683012554513_9073164132726865920_n.jpg   W123 tach-60297681_439220683311283_8896549146165510144_n.jpg   W123 tach-60180242_2144383715597218_6429684119352901632_n.jpg  
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  #2  
Old 05-15-2019, 11:12 AM
Stretch's Avatar
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If you are looking for ends that seem to be hidden in looms and you're not sure where they go the only way I know is to get a multimeter and start performing continuity checks

I assume the wiring loom is still from the 280CE - as in original to the car - so if I were looking for the other end of the wiring for a tachometer on a petrol engined car I'd be off searching around where the alternator sits...

...I've got a feeling (wild guess alert!) that that's how "they" did it for petrol engine cars (not sure why they did it differently for the diesel come to think of it - I'm sure some electrickery genius will jump in and explain...

...another alternative to the alternator way might be via the CIS system that was once fitted where there probably a crank position sensor for the tachometer on the front pulley (that's where it is on my M102 / W201). There's another sensor on the flywheel too on my M102 and the wires all join up on the left hand side of the car near to where the ABS pump on a LHD car is fitted.

As you can tell I'm not up to speed om M110 + W123 engine configurations - hope the comments help enough for you to find the wires.
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1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
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Don't leave that there - I'll take it to bits!
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  #3  
Old 05-15-2019, 12:26 PM
WTB: 94/95 E320 Wagon
 
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When I back-fit a tachometer to my '85 300TD, I just ran all new wiring from the tach amp to the tachometer and to a fuse for power. Left a lot more hair on my head.
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  #4  
Old 05-15-2019, 09:56 PM
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Join Date: Aug 2014
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Thank you. I think i'll just go and buy a new line to put in because i don't want to have to undo and cut open sheathes of wire bundles.

what size/ voltage/amp rating fuse did you use ?
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  #5  
Old 05-15-2019, 11:00 PM
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subscribed .
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  #6  
Old 05-16-2019, 04:11 AM
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Put new lines in today. Last thing i need is a new pickup sensor/cable because the one i have it gone. Reading of 85 Ohms resistance and according to Pierre Hedary anything over about 70 ohms is where failure starts to occure

https://www.youtube.com/watch?v=5glxTyJbgTo

So, I test fitted a blue wire through the firewall along side the standard..

cut what i needed from the plug with as much lead as possible

figured out the wiring.

put a fuse in on the positive line, used a 15Amp fuse, which i think needs to be replaced for a much smaller one..

I think i should put a fuse on the " signal" line as well, not sure.

So yeah, it's time to get a new pickup wire. the grey one that goes to the front of the engine that picks up the signal.

the part number code for it is A 001 153 83 28 for anyone needing it for future reference.
Attached Thumbnails
W123 tach-60335710_2315211995212117_8162666486570156032_n.jpg   W123 tach-60517284_1292154570960091_1822589339360559104_n-1-.jpg   W123 tach-60533027_651181248663009_2626344249209126912_n.jpg   W123 tach-60336376_360909288105827_1200691256154390528_n.jpg   W123 tach-60656146_354635558517158_7793097826493267968_n.jpg  

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  #7  
Old 05-17-2019, 01:57 AM
vwnate1's Avatar
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Question "Too Much Resistance"

? measured where ? .
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-Nate
1982 240D creampuff 370,000 miles
1978 300CD back from the dead&1980 300CD ~ SOLD
1984 300CD KEEPER ! 440,XXX miles
1984 Euro 300TD Fully optioned SWMBO's
1974 350SLC 4 speed stickshift SOLD & missed
Krazy Kommie Ural Motos (3)
BMW Moto R60/6 Barn Find, 8,000miles
1959 VW #113 Deuxe Beetle, 36hp engine, stock
Junk, Rust, Arthritis, Crushed Spine,Broken Neck&Back
Memories, Peace Of Mind
facts & reality don't change because you can't handle them
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  #8  
Old 05-17-2019, 05:52 AM
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there are 3 pins on the signal pickup wire.

1 is the sheilding sheath, the other 2 are the ones you measure across
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  #9  
Old 05-17-2019, 02:50 PM
vwnate1's Avatar
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Post W123 Tachometer Leads

? I thought some were two wire and others were three..... ?
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-Nate
1982 240D creampuff 370,000 miles
1978 300CD back from the dead&1980 300CD ~ SOLD
1984 300CD KEEPER ! 440,XXX miles
1984 Euro 300TD Fully optioned SWMBO's
1974 350SLC 4 speed stickshift SOLD & missed
Krazy Kommie Ural Motos (3)
BMW Moto R60/6 Barn Find, 8,000miles
1959 VW #113 Deuxe Beetle, 36hp engine, stock
Junk, Rust, Arthritis, Crushed Spine,Broken Neck&Back
Memories, Peace Of Mind
facts & reality don't change because you can't handle them
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  #10  
Old 05-18-2019, 08:12 AM
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Posts: 135
Quote:
Originally Posted by vwnate1 View Post
? I thought some were two wire and others were three..... ?

there are 2 kinds of tachs, a 3 wire and a 2 wire. The 2 wire/pin is easier.


Also I was talking about the pickup sensor wire which is 3 pins/wires within it.


Just did a little MS paint to help show what i mean

the end of the sensor wire is a plug which has 3 pins in it
Attached Thumbnails
W123 tach-witing-up-w123-tachometer.png  
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  #11  
Old 05-19-2019, 03:53 AM
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Diesel Dandy
 
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Thumbs up W123 Tachometer Leads

THANK YOU VERY MUCH ! .

One of these days I want to add a tachometer to my '82 240D.....

This document will come in handy when I get a 'roundtuit' .
__________________
-Nate
1982 240D creampuff 370,000 miles
1978 300CD back from the dead&1980 300CD ~ SOLD
1984 300CD KEEPER ! 440,XXX miles
1984 Euro 300TD Fully optioned SWMBO's
1974 350SLC 4 speed stickshift SOLD & missed
Krazy Kommie Ural Motos (3)
BMW Moto R60/6 Barn Find, 8,000miles
1959 VW #113 Deuxe Beetle, 36hp engine, stock
Junk, Rust, Arthritis, Crushed Spine,Broken Neck&Back
Memories, Peace Of Mind
facts & reality don't change because you can't handle them
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  #12  
Old 05-20-2019, 02:30 AM
Benzguy300
 
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I’m want the tachometer to work in my 190 I did a conversion from gas to diesel so it’s not working. I wonder if the same procedures will work ? since the engine it’s different my is a 602 turbo. Anyone knows ?
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  #13  
Old 05-20-2019, 09:52 AM
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Quote:
Originally Posted by benzguy300 View Post
Iím want the tachometer to work in my 190 I did a conversion from gas to diesel so itís not working. I wonder if the same procedures will work ? since the engine itís different my is a 602 turbo. Anyone knows ?
At an absolute minimum you'll have to swap the tach in the cluster. The gas and diesels use a different pulse rate and therefore have incompatible tachs. Not sure about the 201 chassis, but the 124 and 126's with the 603's had the tach signal sent through the EDS/EGR computer before being sent to things like the tach, cruise control, A/C, and radio (in later cars).
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