Speed Pulse on a 190E

[V12]

My car is in a million pieces at the moment, doing some work

One that has stumped me is on the sat nav, the speed pulse...

I'm not too up on electronics, only basic stuff.
But is it a similiar system to the pickup for the cruise control?

I have heard that some of the later W124's have speed pulse, pre-wired behind the radio...possibly a green wire in a black tube?

Any light shed will be much appreciated...

Ricky

 

[RichieRuss2000]

I believe that the speed pulse is usually a wire from the ABS that measures wheel rotation... Good luck finding it, if ABS is unavailable you will need a sensor.

 

[V12]

Hmm, upon further investigation, i have a feeling that it is a green/yellow wire that comes off the back of a little black pack, which is removeable from the speedo head.
The speedo works perfectly with this pack removed.
Is there any way to test with a multimeter if it is the speed pulse? is it just a sine wave?

 

[zerocool]

spped pulse comes off the gearbox normally and goes to the instrument cluster,its the modern way of replacing the speedo cable,would imagine the faster it goes the more current it will generate.
you should have only 2 wires going into the sender unit on the box,1 input wire and 1 output wire,its the output wire that you tap into for your sat nav

 

[andyccr]

Speed pulse testing

Hi All, right to test speed pulse on NON CANBUS cars you will need a multi meter. Most speed pulse signals will either have a range of between 0-4v or 0-12v. To test simply probe the wire and move the car very slowly forward. If you see a 'pulse' of approx the peak voltage then this is normally the speed pulse. Please note this will not always work in reverse.

Andy

 

[V12]

Mine does have speed pulse on the back of the speedo head., to straighten things up a little, it does not come from the gearbox...at least on my car.

The speedo cable comes from the box upto the speedo head, then the little black pack on the back of the speedo somehow converts the mechanical movement into an electronic pulse, which is then used for the cruise control normally.

Thanks for all the pointers.

Ricky

 

[Sp!ke]

Mine does have speed pulse on the back of the speedo head., to straighten things up a little, it does not come from the gearbox...at least on my car.

The speedo cable comes from the box upto the speedo head, then the little black pack on the back of the speedo somehow converts the mechanical movement into an electronic pulse, which is then used for the cruise control normally.

Thanks for all the pointers.

Ricky

Ricky,
I dont suppose you got a photo of the little blighter? It would be handy for others I'm sure.

 

[V12]

Afraid not, should get pics of all the mods i have done on my car, but never think while they are in progress, just too excited! ;-)
Just about to start the first gear pull off relay mod, will get pics!!

But as i understand it, on every car it is different. But can confirm on W201's and W124's the speed pulse is from the back of the speedo, really obvious once you remove the cluster, and on the later 124's 94-96 they have a feed at the radio also.

 

[dieseldes]

IIRC this info is from is what I have learned from my 1988 124 250td , there is a speed sensor fitted to the later cars that have a outside temp guage fitted, when you got below 30mph? it disabled the temp sendor and stored the last reading on the display. I think 1989 onwards.
This was to stop erronious readings due to the heat from the engine compartment.
It probably has other uses as well? My 1990 audi had a speedo output that could be connected to the back of a suitably equiped radio to increase the volume the faster you went.

Des

 

[Surf Blau]

Speedpulse for Navi can be retrieved from a sensor on the back of the instrument cluster, right next to the speedocable. This is originally used for Taxameters, Tempomat and outside-temperature gauge (on later models), and can be bought from Mercedes if not present.

 

[V12]

could have told me that before hand...