1987 O2 Harness Question?

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Here's what I have for Mass Air cars. Maybe someone else will chip in with some information specific to the 87 Mustang.

Diagrams courtesy of Tmoss & Stang&2birds

O2 Sensor wiring harness. Check the part numbers on the drawing against the 87 O2 sensor harness and see if they are the same. If so, the O2 Sensor harness interchange and modification tech note below applies.
mustangO2Harness.gif


O2 Sensor harness interchange and modification

Originally Posted by 302EFI


Revised 16-Oct-2011 to add O2 sensor harness warnings
The wires for the 02's and low oil did not change throughout the years, they are all in the same place.
The main ones you need to worry about are (on the harness end (ECU) that plugs into the 02 plug) is:
\- 1. Lightblue / yellow
- 2. White / Purple
- 3. Purple / Yellow
The White/Purple & Purple/Yellow gets looped for a automatic ECU
The Purple/Yellow & Lightblue/Yellow for a manual ECU

fox-5-0-o2-sensor-drawing-jpg.529445

Not all wires are shown for clarity and simplicity

See Oxygen sensor Harnesses - Manual/Auto differences and year differences - Ford Mustang Forums : Corral.net Mustang Forum for more O2 sensor wiring harness info

Basic premise to use with transmission swaps:
Only run a 5 speed trans O2 harness with an A9L. Do not run an Auto O2 sensor harness with an A9L. Doing so will damage the computer’s internal signal ground.
Only run an Auto trans O2 sensor harness with an A9P in a car that has an Auto trans. Using a 5 speed trans O2 sensor harness with an Auto trans may cause no crank problems.
See Computer issue? | Mustang Forums at StangNet for Joel5.0’s fix to the computer internal signal ground.
The 4 cylinder O2 harness uses 4 wire O2 sensors. It probably won’t work correctly without modifying it.


See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Wiring & Engine Info Everyone should bookmark this site.

94-95 Mustang wiring diagrams
Mustang FAQ - Wiring & Engine Info

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

O2 sensor wiring harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangO2Harness.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pin out
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

87-92 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang87-92 PowerWindowWiring.gif

93 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang93PowerWindows.gif

T5 Cutaway showing T5 internal parts
http://www.veryuseful.com/mustang/tech/engine/images/5_Speed_Cutaway_Illustrated.jpg

Visual comparison of the Ford Fuel Injectors, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/Ford_Injector_Guide.jpg
 
Last edited:
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This is the connector on my 1987, The 87 Mustang had no looped wire for the O2 harness. I have never had an issue using my A9L M.T. computer with this O2 set up and my car has had both the Mass Air conversion and the AOD to 5 speed swap.

The main reason I asked about the O2 harness is that I have read some posts that say any trans swap, you must use the specific O2 harness to the ECU and Trans you are using.

Some have stated that using a A.T. ECU on a M.T. car will cause a hanging Idle when the clutch is pushed in because of the "dashpot delay" programmed into the A.T. ECU. My car idles high for about 5 sec. when the clutch is pressed in regardless of weather I am using the A9L or C3W (A.T.) ECU's. It has never came right down after I did the trans swap when I press the clutch even with the A9L like most factory 5 speed cars do. it's always kind of bugged me but guess I will just have to live with it.

But regardless of that, it looks like I can continue to use my original O2 harness regardless of what ECU I use because my O2 harness is not specific to a certain trans.
012.JPG
013.JPG
 
Last edited:
Here's what I have for Mass Air cars. Maybe someone else will chip in with some information specific to the 87 Mustang.

Diagrams courtesy of Tmoss & Stang&2birds

O2 Sensor wiring harness. Check the part numbers on the drawing against the 87 O2 sensor harness and see if they are the same. If so, the O2 Sensor harness interchange and modification tech note below applies.
mustangO2Harness.gif


O2 Sensor harness interchange and modification

Originally Posted by 302EFI


Revised 16-Oct-2011 to add O2 sensor harness warnings
The wires for the 02's and low oil did not change throughout the years, they are all in the same place.
The main ones you need to worry about are (on the harness end (ECU) that plugs into the 02 plug) is:
\- 1. Lightblue / yellow
- 2. White / Purple
- 3. Purple / Yellow
The White/Purple & Purple/Yellow gets looped for a automatic ECU
The Purple/Yellow & Lightblue/Yellow for a manual ECU

fox-5-0-o2-sensor-drawing-jpg.529445

Not all wires are shown for clarity and simplicity

See Oxygen sensor Harnesses - Manual/Auto differences and year differences - Ford Mustang Forums : Corral.net Mustang Forum for more O2 sensor wiring harness info

Basic premise to use with transmission swaps:
Only run a 5 speed trans O2 harness with an A9L. Do not run an Auto O2 sensor harness with an A9L. Doing so will damage the computer’s internal signal ground.
Only run an Auto trans O2 sensor harness with an A9P in a car that has an Auto trans. Using a 5 speed trans O2 sensor harness with an Auto trans may cause no crank problems.
See Computer issue? | Mustang Forums at StangNet for Joel5.0’s fix to the computer internal signal ground.
The 4 cylinder O2 harness uses 4 wire O2 sensors. It probably won’t work correctly without modifying it.


See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Wiring & Engine Info Everyone should bookmark this site.

94-95 Mustang wiring diagrams
Mustang FAQ - Wiring & Engine Info

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

O2 sensor wiring harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangO2Harness.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pin out
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

87-92 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang87-92 PowerWindowWiring.gif

93 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang93PowerWindows.gif

T5 Cutaway showing T5 internal parts
http://www.veryuseful.com/mustang/tech/engine/images/5_Speed_Cutaway_Illustrated.jpg

Visual comparison of the Ford Fuel Injectors, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/Ford_Injector_Guide.jpg
I wonder about the year 1987 included in this as shown? As you can see by my pics. My 87 has no looped wire on the O2 harness connector nor is it even pinned for one. Was my 87 part of some built without this? Or were all 1897 5.0 models built like this?
 
There is no difference on the non mass air cars.
Since you seem to have some knowledge and interest in this, hopefully you have some input. By looking at the picture, it appears that the OP's O2 harness is not looped.

It is possible that someone modified the original O2 sensor wiring by placing the loop at a different place in the wiring. Or we are looking at the body mating section of the harness opposite were it is looped. What's your call on this?
 
I was reading on the Corral.net Mustang forums site where a OP had posted a thread: Will a A9P computer work with a 5 speed car? Liljoe07 had posted several replies to this post. But another reply to the thread by Neomustangz posted pictures of all the different O2 harness connector plugs used from 87 to 93 and a picture with the one similar to mine said it was the speed density type. For some reason it appears to me that the speed density cars did not need or use the loop wired type and the mass air cars did, I wonder why?
 
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I wonder about the year 1987 included in this as shown? As you can see by my pics. My 87 has no looped wire on the O2 harness connector nor is it even pinned for one. Was my 87 part of some built without this? Or were all 1897 5.0 models built like this?
I also wonder if Joe would know what I would need to do to make my speed density O2 harness compatible to the A9L. What I have seems to function but I would all the proper set up for a mass air, M.T. car ie: matching trans, ECU and O2 harness.
 
Since you seem to have some knowledge and interest in this, hopefully you have some input. By looking at the picture, it appears that the OP's O2 harness is not looped.

It is possible that someone modified the original O2 sensor wiring by placing the loop at a different place in the wiring. Or we are looking at the body mating section of the harness opposite were it is looped. What's your call on this?

No its not modified. That's how the Speed Density 02 harness is supposed to be. On the mass air cars, Ford didn't run the additional circuits through the 02 harness like they did on the mass air cars. The Speed Density wiring completely bypass's the 02 wiring and goes straight to the ECM. So both manual and auto SD cars use the same wiring layout. That's why there is no loop in the 02 harness.

All that is needed to be done for the mass air conversion is laid out here.

Mustang Mass Air Conversion - StangNet
 
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I should clarify that the Auto and Manual SD cars are only wired the same as far as not going through the 02 harness. EVTM's show wiring similar to mass air cars in the other areas. Like Auto's using starter relay ground for Neutral Sensing, and Manuals using SIGRTN. But there is no way I can tell how its done on the EVTM.
 
No its not modified. That's how the Speed Density 02 harness is supposed to be. On the mass air cars, Ford didn't run the additional circuits through the 02 harness like they did on the mass air cars. The Speed Density wiring completely bypass's the 02 wiring and goes straight to the ECM. So both manual and auto SD cars use the same wiring layout. That's why there is no loop in the 02 harness.


At some point in 1988, ford did start wiring the Speed Density cars the same as the MAF cars. My car is a late 1988 speed density car, but with an 8-wire O2 harness with the jumper present. Early 1988's do come with the 5-wire o2 harness, so the change was made at some point during the 1988 model year across the board for all cars, speed density or CA mass air cars