Can I disconnect the o2 sensor by disconnecting its relay?
 

Im curious to test my lean/rich mix and read i need to disconnect my o2 sensor in my 82 SC. Im afraid to touch the weak connection in the back because it may break completely. Can i simply remove the relay under th passenger seat instead?

No. It powers the frequency valve through the jetronic box and the engine will go super lean and run rough.

Beside the fact John mentions in a nutshell, here is what happens:

- Disconnecting the relay under the passengers seat will turn of the whole mixture control driven by the frequency valve, as then the ECU and the frequency valve will have no more power
- Disconnecting the sensor in the engine compartment keeps the mixture control still working but the regulation will be "off" means ECU Switches into an "open loop" state with an middle/average value of 50% duty cycle, here only the CO screw setting affects the mixture, like in case of all other non lambda 3.0 engines.
Disconnecting the sensor in the engine compartment is also done every time an emissions test will be done, so the plug "should" not break . But ... im with you it's one of the worst connections the car was equipped with by Porsche.

I see. ok, I have a replacement connector for the 02, so I guess I need to fix that first!

Thanks all, very helpful!

FYI we do not have emissions test anymore for car older than 20 yrs, at least for NY, is only safety tests (rights, brakes, etc)