o2 sensor question
 

I need to get through CA smog for registering my new to me old '86 944 na. The PO replaced the cat and rusted exhaust pipe sections thinking he could get it passed but gave up on getting the certificate. The smog shop recommended a new o2 because the car was close to passing and felt this was all that is needed. So...I purchased a new Bosh OEM sensor with a three wire connector pin and I find there is an empty pin connector that should mate up just hanging there loose about 12" away from the sensor location. The existing sensor in the car which I am assuming not to be original has a long three pin wire that connects up on top of the engine bay. Now I'm easily confused. Which one is right? Both wires seem to be connected to a legitimate source. Any ideas that could lead down the path to success??

Thanks,
John