Plesae Help With Oxygen Sensor Sorting Out


New Member
Mar 12, 2017
I have a 1987 mustang GT and after rebuilding the engine I am left with a dilemma of sorting out my o2 sensors. My car has a A9L ecu installed by the previous owner and I want to replace the o2 sensors and figure out where a wire goes to. When I went to order original 1987 o2 sensors the color of the wires are different than what are on my car now. Also there is a orange wire sticking up from the bottom of the white salt and pepper shaker 10 pin connector that I am not sure where it goes to. I did some research and it seems to be a ground for the o2 heating part of the o2 sensors. When I turn the key on it is hot and reads 4.7 volts. So I thought that a positive wire showing hot should not be grounded or am I wrong. Also what o2 sensors should I order for replacements. Pictures show what I have in the car now. Any help would be greatly appreciated


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SN Certified Technician
Mar 10, 2000
Dublin GA
The orange wire is indeed a ground. It may show voltage if it is not grounded. Bolt it down to the back of the cylinder head or to one of the lower intake mount bolts.

Don't bother replacing the O2 sensors until you have dumped the computer codes.

Dump codes sticky

Look at the top of the 5.0 Tech forum where the sticky threads are posted. One of them is how to dump the computer codes. Codes may be present even if the CEL (Check Engine Light) isn’t on. You don’t need a code reader or scanner – all you need is a paper clip, or if your lady friend has a hair pin, that will do the job.
I highly suggest that you read it and follow the instructions to dump the codes.


New Member
Mar 12, 2017
Thank you for responding. I want to change out the o2 sensors because when I bought the car it had a hole in one of the pistons and was blowing raw oil through out the exhaust system. It was probably due to the nitrous kit it had which I deleted I completely rebuilt the engine. and it starts and runs fine at partial throttle but very little power past half throttle. I will hook up the wire the way you say and pull codes. After doing some more research I found that different make o2 sensors have different color wires so if I do buy new ones I shouldn't worry? Thanks again


StangNet's favorite TOOL
SN Certified Technician
Mar 10, 2000
Dublin GA
If you specified 87 Mustang 5.0 when you purchased the sensors, the wire color does not matter.
The wire color should be the sensor wiring harness colors, not the actual wire on the sensor itself. The V8 sensors are all 3 wire sensors. The 4y cylinder sensors have 4 wires,
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I want to measure mine. It doesn't look that tall.
10 Year Member
Jul 6, 2006
Bingo. Jrichker nailed it. A 3 wire sensor will plug in only one way.


SN Certified Technician
Aug 27, 2012
In the garage
the only thing that may be screwiing up things is if the prior owner converted it to Mass Air, did he leave the 87 engine and O2 sensor harness, replace them or hack in harness?
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