I am sure that it is coolant level senor. I had the same problem on my 1995 E420. coolant level sensor is located on side of coolant reserviour. If you disconnect the sensor and see if the light goes away. u may also find some coolant leak or rust at the sensor. If you see coolant on terminal replace sensor. if you see rust then just clean the rust.
2005 Triumph Bonneville T100 (Black/white) [Sold]
2007 GL450 (Dersert Silver)
2009 Toyota Corolla (Metallic Silver)
2002 Tundra V8 - 2WD (Desert Sand)
1995 MB E420 (Silver Smoke) [crashed, now resting in peace at Silverstar Recycling Center]