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


New Member
Mar 26, 2018
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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SN Certified Technician
Mar 10, 2000
Dublin GA
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

Complete computer, actuator & sensor wiring diagram for 94-95

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs

Complete computer, actuator & sensor wiring diagram for 88-90 Mass Air Mustangs

Ignition switch wiring

Fuel, alternator, A/C and ignition wiring

O2 sensor wiring harness

Vacuum diagram 89-93 Mustangs

HVAC vacuum diagram

TFI module differences & pin out

Fuse box layout

Mustang 5.0 Lights and Radio schematic, by TMoss:

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

93 power window wiring

T5 Cutaway showing T5 internal parts

Visual comparison of the Ford Fuel Injectors, picture by TMoss:

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

Engine mounted fuel injector harness

Location of the TPS, IAB, and the 10-pin connectors on a 5.0, picture by TMoss:

Starter circuit

Alternator diagram for 94-95 Mustangs.
Last edited:


i'm familiar with penetration
Mod Dude
Feb 18, 2001
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)



New Member
Mar 26, 2018
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.


i'm familiar with penetration
Mod Dude
Feb 18, 2001
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.


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


Mar 4, 2018
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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