View Full Version : o2 Sensor Wiring Help

05-30-2012, 04:56 PM
Long story short.....I discovered that I wore through two of the four wires for my rear o2 sensor.......unfortunately they are on the wiring harness end. Anyway, found a 4 wire o2 sensor plug for cheap and went to hook it up and noticed the wires are different. The wires in my hand are the ones from the cars harness.

Two questions:

-Can I even use this plug being that the wires are different?

-If I can use it, which wires match up?

05-30-2012, 05:01 PM
Plug Wires:

Solid black
Black w/blue
Black w/yellow
Red w/black


Solid red
Black w/red
Black w/yellow
Red w/yellow

FWIW: I've already tried solids together, Black red/Red black, Black yellow/Red yellow, Black blue/Red yellow......because it seemed logical at the time.

05-31-2012, 06:41 AM
If this helps anyone in the future, the torn wires threw a P1040 and P1141.

kung fu jesus
05-31-2012, 06:58 AM
I would love to help, but I don't know what year the car is.

Just from knowing the year, I could go here (http://www.madracki.com/miata/wiring.html).

Then I could find the O2 wiring diagram to see which wire goes where and probably figure out which wire does what.

On a four wire O2, one wire is a signal wire for the O2 (5v, I think), one wire is a switched 12v heater wire. The other two are grounds.

There should also be a wiring diagram that comes with a universal O2 like you bought to help with the wiring.

I hope this isn't reading satirical, I really am trying to help, but you aren't helping yourself without giving the info people need to help YOU.


05-31-2012, 09:25 AM
It's a 2000 :-) I forgot to add the year :-( Never even realized that different years probably had different colored wires.

kung fu jesus
05-31-2012, 10:35 AM

Most universal O2 sensors come with a weatherpack-type connector to splice in the harness. There should also be a wiring diagram with it that describes which wire on the O2 does (signal, ground, power). Do you have that? From that I can tell you which wire corresponds with your car's wiring harness.

On the wiring diagram for your car on the site linked above the wires on the car's harness reads:

RED wire -> 3J on ECU
BLK/RED -> +

kung fu jesus
05-31-2012, 10:51 AM
Oh! Wait! You bought just the plug? Do you know what year Miata it came from? Does the donor plug fit the plug on your car?

05-31-2012, 11:58 AM
Yeah, its the male end from the car that I needed. Hard to come by and expensive from the dealership. After painting my valve cover, I re-mounted in a way that had it rubbing against metal apparently and it cut the wires within 1/2 from the plug :-( I bought the "new" one from Miatamecca salvage store on ebay. It's an "MX5 4 Pin O2 Sensor Male Connector 94-05."

Basically I don't know the year....... Does each year have specific colors? Meaning, is it possible to use the wire colors to determine the year?

05-31-2012, 12:01 PM
If it helps, the inside of the "new" connector is yellow. The one that came off my 110,000 mile car is white inside. Leading me to believe it came of a car older than 2000 .

kung fu jesus
05-31-2012, 01:22 PM
OK. The colors on the donor connector don't matter so much.

Connect the donor plug into your car's female harness. Look at the wires coming out of the female connector, the colors should match the wires you accidentally cut. Take note of which color goes to each terminal on the female connector and write them down in a way you can remember. The connectors can only be joined in a certain orientation, so maybe sketch a profile of the connector on some paper, label each terminal and splice the harness you cut into the pigtail of the donor connector in the corresponding manor.

You could also plug in the male into the female and label (with tape) each of the four wires on the donor part with the color of wire they correspond to on the female side. Remove the donor, splice the cut wires into it, done.

You can also bypass the stock connector altogether and splice the same colored wires together. You would have to cut off the female side.

05-31-2012, 01:45 PM
That's genius! I'll have to wait on this though, as I have an 01+ style header in my car since it was a cali spec, meaning I needed the racing beat o2 extensions. But, thankfully i'm still running the stock o2 sensors so I will pull one and plug it in to the connector to match up the wires. That seems so simplistic now that you mentioned it, thank you!!

kung fu jesus
05-31-2012, 02:33 PM
The wires are difficult to solder, so I would recommend heat-shrinkable crimp-type wire connectors. Wrap them in tape, too, for an added measure of protection from the heat and elements.

05-31-2012, 03:28 PM
sir i do not get power to the spack plag

06-09-2012, 02:58 PM
Matched the wires up today. probably be the end of the week when I post back with the results.

06-10-2012, 04:37 PM
Went for the drive today, Scangauge indicated the car being OBD, emissions ready. No code came back!! Lets hope it stays this way.

kung fu jesus
06-10-2012, 04:37 PM