Thanks, much to the several folks who've assisted me thus far. I'm just about through my LS/Vtec swap (OBDI) into my 89 CRX (DX). (It was previously converted to MultiPoint for my old ZC). I'm down to a few last items. The 4 wire heated O2 sensor is one of them. I can't afford the OEM item but while at a salvage yard picking up some brackets, etc. I scounged up a 4 wire secondary O2 sensor from an EK Civic. I've read that the O2 sensors in OBDII cars are basically the same. The secondary O2 provides a check that the primary O2 sensor is working OK. So I figure I can use a secondary O2 in place of the primary O2. Can I? So my question is, can anyone give me the pin outs of a OBDII 4 wire secondary EK sensor? There are two (2) black wires, a light green wire, and a white wire. Can anyone tell me what is what so I know how to wire 'em up? thanks, Dave K.