Black is signal, white are for 12V heater circuit for the lambda, grey is earth, on the Lambda, I would assume(but check) that on the AFR gauge the red is live, black is signal, grey is earth.
On the lambda the white wires are not polarity concious, as no making so just live on one and earth on the other, the heater circuit in the sensor speeds up the delay in reading
as they don't work till a certain temperature is reached.
tabetha