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.
you might try www.haynes.com, these are the folks that have all the manuals for wiring etc.
The black wires are the heater wires, the white wire is the signal wire and the green is the ground wire.
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.
Could be a diesel? If not then replace your oxygen sensor on your exhaust. A bad oxygen sensor causes the exhaust smoke to be dark in color.
The downstream O2 sensor was broken and is missing the wiring harness, I have a universal O2 sensor, but need the color codes to wire it properly. It has a purple, pink, black and white.
not sure the exact location of the wire in the harness, but i can tell you that the speed sensor has 2 wire leads, that run directly to the PCM. they are in ports 20 and 21 on the PCM wire connector. Pin 20 is for speed sensor low signal and is Light green and black in color. Pin 21 is for speed sensor high signal and is purple and white in color
Which oxygen sensor? There are two of them. They each have 4 wires and each wire has two colors. There were two models of the f250 also, need to know engine size. Sorry.
They are blue, black and white. They can be found extending from the catalytic converter (the upstream O2 sensor) and possibly from a second source (the downstream sensor).
Black for signal, Gray for ground, 2white's for heat
It is used to separate the color burst signal from the color signal.
Oxygen gas has no color. Liquid oxygen has a very slight blue color.
right by the oil filter you should see a gold color one wire sensor.