My mechanic who did mine is not around to ask now... but doing some searching I found this from HotSauce:

Heres what the 4 wires are:

2 are for the preheater.

1 is ground.

1 is signal, and will give a reading of about .95V.

I have no idea what the colors are, but with a DVM it should be easy to figure out.

That being said, I see no reason to have an O2 meter unless you are going to tune with it, and then I'd want a wideband O2 sensor.

John C.