Oxygen sonsor - multiple wires
I'm doing a bunch of stuff to an '89 Ranger, (with 4 cyl engine) i.e. new flywheel, new clutch, new cat converter and pipe. I'm getting ready to put a different exhaust manifold on this truck that I got from a salvage yard. (That's because I couldn't get the bolts out that connected the cat pipe to the manifold. Tried heating, tried drilling. tried bolt extractors, and nothing would work.)
So anyway, this used manifold I got still had an O2 sensor in it. I benched tested it with meter and torch and it passes. My old O2 sensor failed the test. So maybe I lucked out by getting a good sensor with this old manifold. The used manifold (with the sensor) cost $35 which is about what a new sensor alone would cost!
Problem is: this extra sensor has 4 wires but my old one only has 3 wires. Both have the black signal wire, and both have two white wires which I guess are the heater. The extra sensor has a grey wire as well, that being the extra wire.
So my question is: can I use this spare sensor and just assume that extra grey wire is something my truck doesn't use? Or is that a bad idea? I figure it can't hurt to try it.