Oxygen sensor...which wires are which?

[Tishabet]

So I did something stupid.....
I bought a new oxygen sensor for my car, one of the cheaper bosch ones without the Porsche connector. Didn't think twice about it because the PO had installed the same type of sensor and had removed the porsche connectors and connected the wires directly.
Here's my problem: I disconnected the old sensor wires in preparation for removing the sensor, and now I've lost track of which wire is which. It looks like I have a black and 2 whites....I'm guessing the black is the heater wire (?) but I don't know which white on the sensor side corresponds to which white on the car side. Is there some way to tell? Does it matter? For what it's worth, I have a good multimeter and know how to use it, so if there's a way to tell based on resistance or something that would be cool.
Advice greatly appreciated! Thanks!

[Tishabet]

Ah, perfect! Thanks so much for the info and link!

[Ayers]

Hey, FR Wilk is right, the two white wires are the heater. It heats up with current running in either direction. Also, the plug will have two prongs (or sockets, depending on whether you're looking at the one comming from the dme or from the oxygen sensor) that are the same, they are the heater wires. The odd one is the sensor. A single wire oxygen sensor (ie.:cheap) can be used by sticking or splicing it to the odd connection or black wire. It just takes longer to run right when it's cold. It also might go open loop if idling a long time.