Electrical Recently bought an 87 gt..no o2 sensors..need guidance

Drue

New Member
Mar 26, 2018
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Parker, CO
So a little background, this is my first time posting on this forum, I recently picked up an 87 gt project. I grew up working on imports so I don't have a ton of experience with american muscle cars. I've started to tear into the car and I quickly discovered that the car has no o2 sensors hooked up, no "low oil" connection(It's just plugged on the oil pan) and no o2 harness.

I've done some reading and apparently back in the day people used to unplug the o2 sensors because at WOT the computer ignores the o2 sensors but this makes driveability worse. Does this sound right? Car seems to hesitate quite a bit at partial throttle but when you put your foot down to the floor she goes. This is going to be a street car so I need to figure out how to add the 02 sensors and harness. I'm having a hard time even locating where the o2 harness would plug into the main harness in the engine bay, can't find a good wiring diagram anywhere.
 
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jrichker

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The following are diagrams courtesy of Tmoss & Stang&2birds

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring; http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.


TFI module wiring for 94-95 Mustang GT
http://www.veryuseful.com/mustang/tech/engine/images/Mustang-94-95-IgnitionControlModule.gif

Complete computer, actuator & sensor wiring diagram for 94-95
http://www.veryuseful.com/mustang/tech/engine/images/94-95_5.0_EEC_Wiring_Diagram.gif

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 88-90 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

Mustang 5.0 Lights and Radio schematic, by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxLights-Radio_diag.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

Convertible top motor wiring http://www.veryuseful.com/mustang/tech/engine/images/mustang88VertTopMotorCkt.gif

Engine mounted fuel injector harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangEngineHarness.gif

Location of the TPS, IAB, and the 10-pin connectors on a 5.0, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/TPS_IAB_Pic.jpg

Starter circuit
http://forums.stangnet.com/attachment.php?attachmentid=21328&d=1080916057

Alternator diagram for 94-95 Mustangs.
http://www.veryuseful.com/mustang/tech/engine/images/Mustang-94-95-Alt.gif
 
Last edited:

Mustang5L5

i'm familiar with penetration
Mod Dude
Feb 18, 2001
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O2 harness plugs in on the passenger side of the engine bay just ahead of the strut tower under the intake tube. Should be a 8-pin connector with 5 wires in it.

Being an 87, you do not need to concern yourself with o2 jumper pin location as 87 lacked the wiring in the harness. That started in 1988

See this thread for pics of plug end. You'll need to confirm your harness is a 5-wire harness (assuming nobody swapped harnesses from a later year)

https://www.stangnet.com/mustang-forums/threads/1987-o2-harness-question.884039/
 

Drue

New Member
Mar 26, 2018
3
0
1
28
Parker, CO
Great, thanks for your help. So if I do have the 5 wire harness can I buy the harness that fits the 87-93 or do I have to source a specific 5 wire harness from an 87? The only harness I can find online is from american muscle for the 87-93 manual.
 

Mustang5L5

i'm familiar with penetration
Mod Dude
Feb 18, 2001
33,265
9,572
224
Massachusetts
Great, thanks for your help. So if I do have the 5 wire harness can I buy the harness that fits the 87-93 or do I have to source a specific 5 wire harness from an 87? The only harness I can find online is from american muscle for the 87-93 manual.
Ultimately it wont mattery if you have the 5 wire harness. The difference in the harnesses over the years has to do with a jumper wire that isn't present on 1987 Mustangs. So if you picked up a 5-wire + jumper harness, the jumper just connects to empty pins. Won't hurt a thing.

Finding a 5-pin 1987 o2 harness might be tough, but you can easily use any other year harness provided the wiring matches..which it should.

?temp_hash=be118ae297e65d67e3deef9f3d54e77f.gif


Heres the wiring for the harness. The o2 harness is on the left, and the body connector is on the right. On the connection to the body harness, the three pins labeled "771" are the o2 sensor jumper that isn't present in 1987. On the body side, you should have all the wire colors except for those on pins 771, 26 and 199. All the other pins, and wire colors should match up. 5 wires, to 5 wires. 4 are used for the o2 sensors, and one wire (258) goes to the low oil sensor
 

Blotus

Member
Mar 4, 2018
7
5
13
Ron Francis wiring offers this harness. I bought mine off ebay. FH-026 1987-1993 mustang manual trans FH-025 1987-1993 Auto Trans. It comes with configurable jumper and harness is brand new. Going through this myself
 
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