1992 Honda Ascot 02 Sensor maintenance

Engine Performance problem
1992 Honda Ascot 4 cyl Front Wheel Drive Automatic

Hi,
I have '92 Honda Ascot Innova Eng:F20A Chas:CB3. Recently the check engine light came on. The official Honda Dealer and Service centre after $150 told me it was the O2 sensor. They reset the computer/cleared the code and told me to take it away and drive it, if the check light came back on they would know it was the sensor and would replace it for $500.
The light came on again, by which point I had found I could buy the sensor myself for sub $100 and replace it myself, & I purchased it today.
My problem is that the instructions that came with the new sensor (4 wire) are generic and the instructions are:
Join black or purple wire to the ECU output wire
Join remaining two white or black/pink wires (heater). The polarity is not important.
Join remaining grey or fawn wire (ground)
I don't have a wiring diagram for my car to know what the 4 existing wires from the O2 sensor loom are.
My colours are: green, wh, blk, blk
New sensors colours: grey, wh, wh, blk
Plz help me identify the match.