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.

Reply to
Ozmodiar
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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:

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

Reply to
Karl

.....

thanks very much!

Reply to
Ozmodiar
[cruise control amps]

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

Geoff

Reply to
Geoff Miller

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.

Reply to
Richard Sexton

I answered this in my 1st reply: "The ground circuit for the cruise is the brake light bulbs."

Reply to
Karl

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

Reply to
Geoff Miller

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

Geoff

Reply to
Geoff Miller

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