Arthur, that is what I thought, based on my experience with the 190E 2.3-16 and reading the wiring diagrams. But in this case when you disconnect the switch, the resistance goes to infinity, and the fans turn on. I checked the resistance on the "blue switch" with the engine cold, and it is a "dead short" meaning zero resistance. I will check it out today and when it is hot I will make another resistance measurement and let you know what the value is when the fans come on. 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)