Ok, so I've bought an O2 meter as a bit of a tuning aid http://www.3barracing.com/product_3.htm, and need to fit the sensor wire to the sender wire on my lambda sensor. However, the lambda has 4 wires. Apparently I'm after the black one. There are 2 of them! Ideas? Without me bench testing the lambda?

My cars a 1996 SOHC non vtec 2.2ies Accord Aerodeck (F22B5 motor)