W126 Rev Counter not working

[S11YBM]

Since I've had my 84 500 SEC the rev counter has never worked. Anyone have any ideas what it can be? I've yet to pull out the cluster to see if all is good there, but before I do that I wanted to check everything else.

I cannot figure out where the rev counter gets its signal from....

 

[S11YBM]

not sure if this thread should be here or in the engine section....

 

[grober]

the electronics section? signal wires are normally green yellow in that vintage of car the tach signal wire will probably come from pin 1? on the diagnostic socket mounted on the inner wing somewhere- that in turn will get the signal from the ignition unit. The tachometer dash unit unit [ solid state] will also have a power supply lead [ colour unknown -possibly black/red and an earth [brown] you will need to pull the einstrument cluster to see the connections.

 

[S11YBM]

the electronics section? signal wires are normally green yellow in that vintage of car the tach signal wire will probably come from pin 1? on the diagnostic socket mounted on the inner wing somewhere- that in turn will get the signal from the ignition unit. The tachometer dash unit unit [ solid state] will also have a power supply lead [ colour unknown -possibly black/red and an earth [brown] you will need to pull the einstrument cluster to see the connections.

Thanks grober. I was just reading that pin 2 is ground right? So I can measure to see of I get a voltage between pin 1 and 2?

 

[grober]

AFAIK the tach is just a voltmeter and if referring to the diagnostic connector pins 1 and 2 [ assuming pin1 is signal and pin 2 is earth- you need to check this] you should get a voltage that will vary up and down with the engine revs. If present at the diagnostic connectoryou need to check for same at the tach connection end.

see this pdf for a contemporary SL

https://www.startekinfo.com/StarTek/outside/11883/PROGRAM/ETM/83etm.pdf

this might help also
http://www.benzworld.org/forums/9693449-post8.html

 

[gbjeppm]

Pulling the cluster is easy on the SEC.

MB have special tools, but I just use a wire coat hanger, cut into two pieces about 25 cm long with a 1cm right angle bent into the end.

Slide down each side, twist and pull. It is only wedged in, not clipped in. While you have it out, I would take the opportunity to replace the bulbs, made a big difference to me.

 

[grober]

https://www.youtube.com/watch?v=KLokBcbhhF8&feature=youtu.be

 

[S11YBM]

Pulling the cluster is easy on the SEC.

MB have special tools, but I just use a wire coat hanger, cut into two pieces about 25 cm long with a 1cm right angle bent into the end.

Slide down each side, twist and pull. It is only wedged in, not clipped in. While you have it out, I would take the opportunity to replace the bulbs, made a big difference to me.

Thanks for that! Could I be a pain and ask what bulbs you used?

 

[S11YBM]

AFAIK the tach is just a voltmeter and if referring to the diagnostic connector pins 1 and 2 [ assuming pin1 is signal and pin 2 is earth- you need to check this] you should get a voltage that will vary up and down with the engine revs. If present at the diagnostic connectoryou need to check for same at the tach connection end.

see this pdf for a contemporary SL

https://www.startekinfo.com/StarTek/outside/11883/PROGRAM/ETM/83etm.pdf

this might help also
Mercedes-Benz Forum - View Single Post - Missing Pin 3 on 8-pin Diagnostic Connector, How To Check CIS Codes?

So I have voltage change here, when the engine is revved there's a change, which is a good sign, next step I'll remove the cluster

 

[grober]

TACH part no you require [ ASSUMING ITS BROKEN] would be either A0025423216 up to PROD NO A0411952 or A0025427116 thereafter. Common to 380,500 SEC and saloons with same engine I believe

 

[S11YBM]

TACH part no you require [ ASSUMING ITS BROKEN] would be either A0025423216 up to PROD NO A0411952 or A0025427116 thereafter. Common to 380,500 SEC and saloons with same engine I believe

Thanks Graeme, is the part number you quoted for the tach it self?

 

[grober]

The tach assembly which includes the clock and its adjuster mechanism.
viz
Drehzahlmesser Uhr Kombiinstrument TOP Mercedes W126 SE SEL SEC 0025423216 | eBay

 

[S11YBM]

Hey guys!

Finally I pulled out the cluster to change the bulbs and try to get to the bottom of the rev counter not working!

Any pointers in what could be faulty in the tach assembly? The clock doesn't work either...not sure if thats related...

 

[ianrandom]

Never known the tach not to work. The clock not working is normal enough though, they always seem to be to expire at this age.

 

[S11YBM]

Never known the tach not to work. The clock not working is normal enough though, they always seem to be to expire at this age.

Yep, rather annoying! When I took tach out the silver middle has lots of greyish corrosion on it not sure whether that effects it.....

 

[stwat]

I take it you have checked and cleaned the fuses?

 

[S11YBM]

I take it you have checked and cleaned the fuses?

I did clean and check all the fuses, but will double check. Do you know what fuse is for the tach?

 

[S11YBM]

Crisis over! After cleaning the contacts on the cluster the rev counter is now working!! The clock is still not working, which I can live with! Like someone said, if I was working every second for the last 30 odd years, I'll prob stop working too