Eric,

Once again if my 240D was here I would check it to make sure, but the car is not available. However, there are a number of different cruise control systems used on 240D's, from model year to model year, or even within model years. For example, none of the throttle linkage hardware connecting to the cruise control, or the actuator, is the same on my father in law's 1980 240D.

I am reasonably certain the sensor at the crank is the cruise speed signal because on my car I pressure washed the engine and blew that little sensor off its mount, and the cruise system stopped working. Since it was the only thing that stopped working, I was pretty sure it was the cruise speed input signal.

240D's to my knowledge did not have tachs, and Diesel tachs on 300D's are driven by a signal from part of the drive to the oil pump. I cannot imagine what the sensor at the crank is for if not to measure crank speed, and on a 240D from this era, there is not much to do with an electrical signal of crank speed, other than use it for cruise control. Good luck figuring this nest of loose wires out.

Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)