I've checked my W126 & W124 manuals & CD's, and it looks like I can adapt the W126 electronic speedometer to work in my W124 instrument cluster.
However, I cannot find either the electrical schematic for the speedometer-to-transmission, nor information on the "black-box" that attaches to the transmission to send the speed signal.
I have a tranny from a 1995 C36 (722.328) and need to know if I can retrofit the W126 tranny speed-sender, and also not adversely affect any other systems.
I'm leaning towards no adverse affects due to the AMG M104 engine using an electronic accelerator and the ABS supposedly not linked to the speedometer.
I'm doing this because even with a new speedometer cable and rebuilt speedometer gauge, I just don't get the smoothness of operation of an electronic speedometer.