The speed signal that the cruise uses is generated in the transmission's tailshaft. If you've got a 124/123/201 that is all mechanical up to the back of the speedometer. The 126 and others are electrical from the transmission.
The easiest place to pick up signal would probably be at the cruise amplifier. Pin 11. Square wave. Peak to peak voltage = battery voltage. I'm not sure how much current is provided so if you're hooking up to something that could draw current, I would pass the signal through a buffer of some sort.
LNG, I replied
The click-to-click method is about all i got. It seems to be fairly consistent on my 190E as for numbers..
Most of this is driving at 60-65mph or 70-75. Only like 10 miles of each fill-up is in town driving.
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