Continuation from here...I was making a mistake on my initial test method so I want to start a fresh thread so it does not get confusing.

1987 260E.

I was checking the o2 sensor with (+) and grounding the other side...Stupid. So I ran it INLINE this time (this IS the correct way to do it right?)

Car warmed up: 0.48v....stuck there. It does not change.
Since this was fishy...Next I unplugged the sensor completely. No O2-sensor light illuminates on cluster. The bulb is fine because it illuminates during ignition.
So why would I get no check engine/o2 sensor light when the sensor is disconnected? It is obvious this has nothing to do with the sensor I spliced in because regardless, if the sensor is disconnected I should get the CE light.

Now I am completely lost on where to go.

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