schurmann

In a '89 300SE, gas engine, I've got the cooling system warning light flickering and glowing dimly when I first start the car (cold engine) and it just stays like that all the time.
The temp gauge shows I'm not running hot, everything fine: 85-90 degrees celsius, but even on a cold engine in the morning before it warms up at all it's on and flickering like a lose wire.
I'm thinking it's a bad sensor since temp doesn't seem to be a factor.
Can someone tell me where the SENSOR for this warning light is?

Maybe I just need to clean off corrosion or something?

Thanks!