The w/s washer resrevoir sending unit is tied to the coolant level sending unit in series. If either goes open or short circuit then low coolant lamp comes on!! The w/s washer reservoir sending unit is a common failed part, esp with high levels of w/s antifreeze in the reservoir.

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MERCEDES BENZ MASTER GUILD TECHNICIAN
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. Shopforeman
190E 2.3 ITS RACECAR
1986 190E 16V