I'm working on an EJ swap into a '78 and I'm having a bit of trouble figuring out how to connect my rear O2 sensor.  

The two O2 sensor connectors in my wiring harness - from a '97 impreza - are one that's female, white, that clips right in on the first 02 connector.  But the connector for the rear sensor is male and dark grey with 4 pins.  Everything I've found for the extension harnesses should also plug right into another female so I just got two and spliced a female to the male end thinking it would plug right in and go, however, the grey connector doesn't even mate to the white female connector.  So then I thought I'd cut it off and splice on another white male connector however the wire colors are not the same layout.  

No one local seems to be able give me any info here and was wondering if someone on the forum might be able to.  

 

The one I cut out of the '97 harness is on top -grey - you can see they're not the same.

 

 

The wire colors from top right corner and going clockwise incase you can't tell are:

Grey Connector:

YR, W, Y, BrownWhite

White Connector:

WB, Kind of a dark Green maybe Blue, W, YR

 

As you can see, the wire colors are not arranged in the same way on the connectors and not all 4 are the same.  Can any one figure this for me?

There were several variations of rear o2 sensor connectors during that time. To make it work you have to match the o2 sensor and rear harness to the year that main harness came from.

A 95 harness was different from a 96, and 96 is likely to be different from 97.

And a Legacy harness was different from an Impreza.

I know that the O2 sensor and the wiring harness match (from the same car), I just don't have the original extension wiring piece and can't seem to find a match.  

Edited December 3, 201312 yr by julianco

Right, that can be the tricky part. I found out the hard way as well after trying two different harnesses on my 95 legacy. Don't know how but I lost the original while I was replacing the transmission some time ago. Got two from a junkyard (on separate occasions) and neither fit, and they were both different. Had to find a 95 to get the right harness.

Right.  Well I'll be searching Denver area junkyards I suppose....