1986 325es O2 Sensor Wire Harness

[ryder]

I purchase a '86 325es back in February and I am now just getting to working on it.

I just noticed that the O2 connector that is secured under the unused battery tray is not connected.

I found the cable coming from the O2 sensor nearby in the engine bay, but it only has 3 cables/pins on it and is not the same size as the larger circular connector, which has 4 cables/pins.

I have a O2 harness from a 325is O2 sensor with connector I can use to complete the connection between the two cables but I am not sure how to wire it.

The harness from the O2 sensor has 3 wires (blue, green/blue, and brown).

The circular connector has 4 wires (green/blue, brown, an additional brown wire, and a black wire). The additional brown wire and the black wires are shrink tubed together but connect to separate pins on the connector.

I also found a cut harness/plug under the hood. (3rd pic). Looks like it could probably be part of the wiring also.

Does anyone know how I can connect the harnesses or can provide a pic of their harness I can use for reference?

Since both connectors are extremly different, I am guessing I may be missing a plug between the two connectors.

The only thing I can assume right now is that the both green/blue wires need to connect.

[reelizmpro]

I'm confused. 86 325eS should have a 3 pin harness for the oxygen sensor. I'd like to find out why you have a 4 pin harness in your engine bay. Was the engine harness swapped? Sounds like the previous owner did some swapping.

[ryder]

Maybe. I wish I knew. He's a good friend of mine so I have called him about it, but he says he doesn't remember. The car was sitting for 5 years.

[ryder]

The only thing I see that doesn't look oem under the hood is this Miller intake piece.

[ryder]

Would I be able to just use the 325is O2 sensor I have and make the harness long enough to reach the under hood connector?

[reelizmpro]

Looks like you have a late 325i engine with Miller MAF conversion. If the wiring is short, you probably are using the old 325e exhaust system. The 325i system has the oxygen sensor in the down pipe if I remember correctly. Yes, remove the 3 wire and install the 4 wire 325i sensor. Ideally, you'd want the 325i exhaust setup which moves the sensor closer to the engine so you won't have to extend any wiring.

[ryder]

Thanks. I'll try that tomorrow.