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Car Forum / Mercedes-Benz Cars / October 2006

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W126 Cruise Control Amp

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Ozmodiar - 28 Sep 2006 17:50 GMT
should the cruise control amp from a
1983 W123 300D Turbo work in a
1984 W126 300SD Turbo?

they have different part numbers and different color plastic at the
connector, but they both accept the same cable.

i had (what i thought was) a good cc amp from my old W123 and it did not
work in the W126.

thanks.
Karl - 29 Sep 2006 02:23 GMT
No, they will not swap. The difference is the resistance value built in for the length of the wire
going to the stop lights. 126 is longer than 123.
Why does this matter, you ask? Simple. The ground circuit for the cruise is the brake light bulbs.
The resistance of the filaments and the wire to them is X value. When you step on the brake, the
ground goes away [the stop lights light up].

MB got smart later on and made the same cruise amp for all. And added a resistance plug to plug in.
The coding plug is different for each model.
As an example, go here:
http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=124133%5F15S&M=603%2E960&GA=722%2E35
7&CT=F&cat=15S&SID=54&SGR=750&SGN=22


and scroll down to the 2nd picture.  137 is the 'universal' amp. 140 is the specific coding plug.

> should the cruise control amp from a
> 1983 W123 300D Turbo work in a
[quoted text clipped - 7 lines]
>
> thanks.
Ozmodiar - 30 Sep 2006 11:00 GMT
>> should the cruise control amp from a
>> 1983 W123 300D Turbo work in a
>> 1984 W126 300SD Turbo?

> No, they will not swap. The difference is the resistance value built in
> for the length of the wire
> going to the stop lights. 126 is longer than 123.
.....

thanks very much!
Geoff Miller - 30 Sep 2006 17:54 GMT
"Karl" <aufever@prodigy.net> wrote:

[cruise control amps]

> No, they will not swap. The difference is the resistance
> value built in for the length of the wire going to the stop
> lights. 126 is longer than 123.

What do the stop lights have to do with the cruise control system?

Geoff

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Richard Sexton - 01 Oct 2006 09:34 GMT
>"Karl" <aufever@prodigy.net> wrote:
>
[quoted text clipped - 5 lines]
>
>What do the stop lights have to do with the cruise control system?

The cc is kicked off when the currend is sensed going through the brake
light bulbs. This is also why it's important to use the correct German
bulbs back there that absolutley have the right resistance.

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  Need Mercedes parts?   http://parts.mbz.org
Richard Sexton       | Mercedes stuff: http://mbz.org
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Geoff Miller - 01 Oct 2006 23:34 GMT
> The cc is kicked off when the currend is sensed going through
> the brake light bulbs.

Interesting; thanks.  I knew the CC disengaged when the brakes
were applied, of course.  But I'd always thought that was done
with a switch underneath the brake pedal arm, kind of like the
downshift switch that's underneath the accelerator.

Geoff

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"There is one evil which...should never be passed over in silence
but be continually publicly attacked, and that is corruption of
the language..." -- W.H. Auden

Karl - 01 Oct 2006 15:14 GMT
I answered this in my 1st reply:
"The ground circuit for the cruise is the brake light bulbs."

> "Karl" <aufever@prodigy.net> wrote:
>
[quoted text clipped - 7 lines]
>
> Geoff
Geoff Miller - 01 Oct 2006 23:37 GMT
> I answered this in my 1st reply:
> "The ground circuit for the cruise is the brake light bulbs."

I didn't see your first reply, hence my question.

Geoff

Signature

"There is one evil which...should never be passed over in silence
but be continually publicly attacked, and that is corruption of
the language..." -- W.H. Auden

 
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