Exhaust Sensor(?)
 

While cleaning the wheels on my '83 500 SL, I noticed a red wire was loose under the car. Upon inspection the wire originates at a sensor(?) located in the exhaust header pipe(the two pipes that that go down from the manifold) on the passenger side. I traced the wire into the engine compartment and it is not attached to anything. Does anyone know what this sensor and wire are supposed to be doing? The car runs great.

my first reaction is that it is a O2 Sensor but I don't know if a car with that age has O2 Sensors. The O2 sensor is used for emission control

It's the O2 sensor. Should be plugged in somewhere.

You could put a voltmeter on it and see if it's working. Once the car is warmed up, it should vary around 1V.

best,

Dave