W126 Cruise Control Amp

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.
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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 4133%5F15S&M`3%2E960&GAr2%2E357&CT=F&catS&SIDT&SGRu0&SGN"
and scroll down to the 2nd picture. 137 is the 'universal' amp. 140 is the specific coding plug.

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.....
thanks very much!
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[cruise control amps]

What do the stop lights have to do with the cruise control system?
Geoff
--
"You might be a redneck if you think the last four words to the Star
Spangled Banner are 'Gentlemen, start your engines.'" --Jeff Foxworthy
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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.
--
Need Mercedes parts? http://parts.mbz.org
Richard Sexton | Mercedes stuff: http://mbz.org
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Richard Sexton <See http://rs79.vrx.net for address> writes:

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
--
"There is one evil which...should never be passed over in silence
but be continually publicly attacked, and that is corruption of
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I answered this in my 1st reply: "The ground circuit for the cruise is the brake light bulbs."
wrote:

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I didn't see your first reply, hence my question.
Geoff
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but be continually publicly attacked, and that is corruption of
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