I think its the purple wire coming from the Oxygen sensor!
The oxygen sensor is connected by a wiring harness. The wiring harness contains the signal wire. The signal wire goes to the system computer.
you can breath
The black wires are the heater wires, the white wire is the signal wire and the green is the ground wire.
I believe it is the black wire coming from stock o2 sensor. I have tested this wire with votmeter and have seen voltage fluctuation from 200 mv - 900mv. I think this is correct.
The signal wire should be Tan. You should have a Yellow, Black, and Tan Wire. The Yellow being you MAF Sensor Signal. The Black being a Low reference voltage. Then your Tan your IAT sensor signal.
get the right oxygen sensor
you might try www.haynes.com, these are the folks that have all the manuals for wiring etc.
Reassure the resistor of the hot wire anenmeter to determine if it has failed. This can be done at the same time that you test the oxygen sensor.
You would need to get a digital multimeter and check the voltages with the key on to determine which is which. I presume you can see the wires at the connector on the O2 sensor and trace them back to the break. The dark green wire with the orange stripe is +12 volts heater positive. The black wire is ground and heater negative. The black wire with the blue stripe is your reference voltage. It should be less than +5v The black wire with the dark green stripe is the signal return and the only one left. Your only other choice would be to get a wiring harness diagram and trace the continuity back to the connector on the ECM.
Cut the wire, unscrew the old oxygen sensor then replace it with the new one and finally, connect the new wire, making certain that you follow the manufacturers wiring diagram. To find the oxygen sensor, look at the exhaust manifold, then follow it down to where the manifold feeds into the headpipe. The oxygen sensor is the part that screws into the exhaust and has a wire connected to it.
the oxygen sensor is grounded when you thread it into the exhaust manifold the oxygen sensor should have only 1 wire it should be purple the didnt start putting 2 or 4 wire sensors in until the early 90's there should be a ground from the battery to the block