Fox 87'-88' Vs. 89'-93' Factory Wiring Harness

BOSS_289 · Nov 14, 2015

I'm a new member here and this is my first post, so please go easy on me. lol

Question #1 -
I have a 91' Mustang GT with a Cobra Motor and T5. I am going to move everything over into a 88' Mustang Convertible that I bought which is extremely clean, straight and rust free. It's got a 4 banger Automatic currently in it.

My questions is are the main wiring harnesses the same? I am going to pull the engine harness with my drive train currently in the 91', but wondered is the PCM (A9L) will match up with the wiring harness in the 88'.?

Question #2 -
I have been reading up on the Moates and SCT Chips and Tuning Software. I have another engine build almost done now, which is bascially a Boss 289 (289 crank cut for 1pc rear main seal, 289 rods, 351C Forged Dome Pistons, 302 Roller Block, 351C-4V heads machined to 302 block/intake) and will be trying this out with my current EFI (using PME intake adapter plates). With this in mind, which product do you recommend, or is there another product along the lines of "SpeedBrain" that would be a better fit?

stykthyn · Nov 14, 2015

You are going to need to swap at least the dash, eec, headlight, and o2 harnesses. Not sure if the fuel pump wiring is compatible or not so be ready to move that as well.

90sickfox · Nov 14, 2015

Look up dirtydirtyracing .com and send Willie lynch a message or call them. He does great work with moates quarter horses and can explain everything to u.

90sickfox · Nov 14, 2015

The issue with the body harnesses is your 91 has air bags the 88 doesn't. You'll have to swap both harnesses...so...everything has to be swapped. The only thing that's the same is the wiring for the lights and locks. The gauge cluster will have to be swapped along with the steering column and the pedal assembly. Its not hard to pull the dash...actually makes it a lot easier to swap the pedals. You don't have to remove the wiring harness to get the dash out. Pull it together its easier. The body harness runs through the drivers side into the engine bay....the engine harness runs from the passenger side into the computer. Good luck.... Keep us posted.

BOSS_289 · Nov 15, 2015

Thanks for all the input.

I've got a few other things with this setup I'm moving over that aren't straight forward. This 91' is currently running a Toyota 1.4L SC-14 Supercharger. After getting this thing home, I started giving things a closer look over and found that the MAF Meter is non-existent. So I called this guy back and asked him how it was idling and driving good without it. He told me that it had a "Piggyback Chip" that he bought through Americanmuscle,com . It made sense. I live in a water front condo and the HOA in here is like a Max Security Prision, lol. I pop the hood to check the oil, and I have someone complaining. So I put my mustang in storage. Months go by before I get new engine build parts finished up at the machine shop and am ready to start changing stuff. So I pull the PCM (A9L) and open it up to find NO CHIP, it's BONE STOCK. So, I am guessing that it had some SCT tune to the factory PCM.

The car is an Alabama Rebuild, re-titled in Florida by the previous owner. The wiring in the PCM kick panel is a bit rough/chopped/spliced up. With this in mind, would I better buying something like a "Painless Wiring" setup, or pulling/buying a stock wiring harness to put in the 88' and leave this alone so I have something to go back to and look at later if I run into issues??

I'm color blind, and have been a old school Mustang most of my life. So, as much as I enjoy saving some $$$ when/where I can, I also like to keep it as simple as possible too.

BOSS_289 · Nov 15, 2015

Here's inside the A9L

jrichker · Nov 15, 2015

Being color blind, you have a major problem; all of the wiring is color coded. The wire colors changed from year to year. The 87-90 use the same color scheme but the 91-93 use a different color scheme. To make it worst, the 92-93 Mustangs have the same fuel pump components but a entirely different fuel pump circuit.

Copied from bbunt302
Just for reference, here's a list of all the compatible years:

89 harness should work for 86-89 as long as you're using mass air.
90 harness will only work in a 90. (because of air bags and dual dash connectors)
91 through early 92 harnesses should be compatible (single dash connector, fuel pump relay under driver's seat)

Late 92 through 93 harnesses may be compatible (single dash connector, fuel pump relay under the hood). You may end up running some extra wire for the fuel pump relay. Comments and input from someone who has actually used the 92-93 EFI harness would be nice.

MAF information:
Swapping the MAF sensors between different MAFs is a big no no. The MAF body and sensor are designed to match each other. Therefore you can't swap sensors between different part number MAF bodies and maintain proper calibration. The assembly is designed to match the computer’s internal program, and swapping a different MAF can upset the computer's calibration.

The OEM Ford MAFs are not calibrated to injector size. The injector sizing is done in the computer’s internal programming. Aftermarket MAF’s “lie” to the computer in an attempt to fool the computer into changing the injector pulse on timing to match the increased airflow.

The exception to the above statements is if you have an aftermarket tuner system such as Moates Quarterhorse, Tweecer, or similar device. Then you can alter the computer's MAF transfer function table to match whatever MAF housing and sensor you have. The tuner device works in conjunction with a high quality Air/Fuel ratio meter so that you can tell what sort of air/fuel mixture you have a any given time.

Some helpful links:
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

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 tang/tech/engine/images/mustang88VertTopMotorCkt.gif

90sickfox · Nov 15, 2015

Get a painless wiring harness for the a9l computer. Simpler in the long run. The body harness in the car should still run lights and such. Either way painless support can help you out. Good luck man.

BOSS_289 · Nov 15, 2015

90sickfox said:
Get a painless wiring harness for the a9l computer. Simpler in the long run. The body harness in the car should still run lights and such. Either way painless support can help you out. Good luck man.

Thanks, I'm going to give them a call in the morning.

BOSS_289 · Nov 15, 2015

90sickfox said:
Get a painless wiring harness for the a9l computer. Simpler in the long run. The body harness in the car should still run lights and such. Either way painless support can help you out. Good luck man.

Thanks, I'm going to give them a call in the morning.

BOSS_289 · Nov 18, 2015

90sickfox said:
Look up dirtydirtyracing .com and send Willie lynch a message or call them. He does great work with moates quarter horses and can explain everything to u.

I spoke with Willie @ dirtydirtyracing.com ( QH with base tune and Innovate wideband combo [QH,tune,wideband] - $589.99 : Dirty Dirty Racing, Vehicle EFI Dyno & Street Tuning )

This guy is a walking racing dictionary, lol. He had me fixed up with what parts I need, and explained everything in about 15 mins of conversation. I will be buying the "QH with base tune and Innovate wideband combo" from him, as he offers a dial-in tune as part of the sale. Nice guy, friendly and knowledgeable. I'll be sending all my buddies to him for their EFI needs.

He also put me onto "MPS Auto Salvage" ( MPS Auto Salvage - your best resource for Ford Mustang Parts New and Used Ford Mustang parts ) for my harness questions/issues. As they offer used OE wiring harnesses with a warranty for foxbody mustangs. And they have a guy in staff that does nothing but mustang harnesses. He pulls the harnesses out of salvage vehicles, inspects them, and makes whatever repairs needed to resell them with the warranty.

I will keep you posted as I make progress with my build.

90sickfox · Nov 18, 2015

Great man ! Glad to help... He always helps me out with no problem at all. They've got a really good thing going on over there.

mikestang63 · Nov 18, 2015

BOSS_289 said:
I spoke with Willie @ dirtydirtyracing.com ( QH with base tune and Innovate wideband combo [QH,tune,wideband] - $589.99 : Dirty Dirty Racing, Vehicle EFI Dyno & Street Tuning )

This guy is a walking racing dictionary, lol. He had me fixed up with what parts I need, and explained everything in about 15 mins of conversation. I will be buying the "QH with base tune and Innovate wideband combo" from him, as he offers a dial-in tune as part of the sale. Nice guy, friendly and knowledgeable. I'll be sending all my buddies to him for their EFI needs.

He also put me onto "MPS Auto Salvage" ( MPS Auto Salvage - your best resource for Ford Mustang Parts New and Used Ford Mustang parts ) for my harness questions/issues. As they offer used OE wiring harnesses with a warranty for foxbody mustangs. And they have a guy in staff that does nothing but mustang harnesses. He pulls the harnesses out of salvage vehicles, inspects them, and makes whatever repairs needed to resell them with the warranty.

I will keep you posted as I make progress with my build.

Willie is a great guy, ask for Billy at MPS- he will do you right. bought my seats from him about 6 months ago.

sprayhappy · Nov 25, 2015

I've never seen a supercharger set up like that

madspeed · Nov 25, 2015

Willie did the tuning on my old turbo fox, highly recomended

Mustang5L5 · Jan 5, 2016

That's not a cobra motor. A9L and I see orange top injectors. Looks like a stock 5.0 HO with just Cobra intake on it. Of course, then there's that supercharger which I have no idea how that's setup without a MAF

Honestly, seems easier to swap the engine into the 1988 and just do a Mass air conversion to it. The harness kit from IST harness is only $45 or so. Seems easier than rewiring things.

a91what · Jan 5, 2016

Personally I love my megasquirt setup. Just got back from Data logging, still building my tune. Anyway love the build! What intake is going on that boss 289???

Oh and some of us do crazy stuff all the time, this is my Frankenstein.with m90

a91what · Jan 5, 2016

Lol. I finally scrolled up and looked at the pics again. Nvm on what intake

BOSS_289 · Jan 8, 2016

a91what said:
Personally I love my megasquirt setup. Just got back from Data logging, still building my tune. Anyway love the build! What intake is going on that boss 289???

Oh and some of us do crazy stuff all the time, this is my Frankenstein.with m90

I like that setup! What cam are you running in that?

BOSS_289 · Jan 8, 2016

Mustang5L5 said:
That's not a cobra motor. A9L and I see orange top injectors. Looks like a stock 5.0 HO with just Cobra intake on it. Of course, then there's that supercharger which I have no idea how that's setup without a MAF

Honestly, seems easier to swap the engine into the 1988 and just do a Mass air conversion to it. The harness kit from IST harness is only $45 or so. Seems easier than rewiring things.

The 88' Convertible is 4cyl/AT car. If I swap the 5.0HO into it, would I need to get a Speed Density engine harness to go along with the MAF Conversion Kit? And which computer would I then run??

Fox 87'-88' Vs. 89'-93' Factory Wiring Harness

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