02 senor question

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Finally got my sr running, blacktop s13, but when I received the car, the 02 senor wiring was cut at the back of the o2 senor, and theres no plug, its spliced directly to the harness.. I purchased a new 02 sensor, and was wondering which of the other two wires do, im assuming one is a ground, which is probably the thick black wire, and the other wire is a +12 volt switched, but the new o2 senor has one wire.. =( Any suggestions?