W126 Cruise Control Amp

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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thanks very much!

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

Geoff

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.

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

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

Geoff