The low coolant light stays on with plenty of coolant in reservior. No corrsion around pins, I pretty much got them clean.

Tested Ohms on sensor and with coolant hot it was about 400 ohm. What should it be? I would like to confirm that sensor and not connector is the problem before I change.

This is common. I had the same problem with my 87 300E.

If the water level is fine, you unplug the wire to the sensor and the light goes out, then there is nothing left to be bad but the sensor.

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02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)

This problem happen once before a few years ago and it turned out to be the connector. It had a fair amount of corrosion on it. After I cleaned it off the light went off.

That's why I was thinking maybe it was the connector. There is no continuity between the two wires on the connector, in other words when I check it with the ohm meter there is not a complete circuit. Should there be?