[Nathandyke]

Hi I have a 1991 mustang lx 4 cylinder coupe that I have basically completed an entire swap on the only thing left is to get it wired up correctly. Currently I have everything working as far as I can tell except for I am not recieving any signal to my fuel pump or to my ingnition coil. After reading through this thread it has become apparent that ford changed some of the wiring around through the 1987-1993 years. I am the kind of guy that likes the challenge and learning opportunity of this kind of stuff not to mention the sense of pride when I can solve a problem. I was wondering if anyone could help me out with finding the wiring diagrams I need to be able to fix this little problem. Also I am not against swapping harnesses if that is what is required however the only ones I have found for sale so far run in the 600 to 1000 dollar range and for that kind of money I would rather get a better understanding of how my car works for future reference. Thanks for your help. Nathan

 

[89coupe]

What harness do you have now?

 

[Guest]

5.0 Wiring Harness --- 87-95 Wiring Changes

87-95 Wiring Changes - There are several different harnesses Ford used on the 5 liter Mustangs. If you are doing a conversion or need a replacement harness, here are the differences in the harnesses by model year.

Year: Details:

1987-1988 - Speed Density. All the speed density engine harnesses are interchangeable. Ford used a different computer in 86, but the engine harness is the same. The dash harness in the 86 is specific to that year car and will not work in the 87-93.

1989 - Mass Air and No Air Bag. One year only harness. Only car with mass air and no air bag. The dash harness is the same from 87-89 on all models, but the engine harness is specific to the 89. The 89 harness can be used in place of the stock 87-88 harness for anyone looking to do a mass air conversion.

1990-1992.5 - Mass Air with Air Bag. Fuel pump relay is under the drivers seat. The change here was made sometime in 92. All the dash harnesses for all models from 90-93 are interchangeable.

1992.5-1993 - Mass Air with Air Bag. Fuel pump relay is in the engine compartment. M12071C302 is this style engine harness. All the dash harnesses for all models from 90-93 are interchangeable.

1994-1995 - All the engine harnesses from the 94-95 V8 cars are interchangeable. All the dash harnesses from the 94-95 cars are interchangeable.

 

[Nathandyke]

I believe I have a 1989 engine harness. The dash harness is 1991. If you have a pin diagram or know where I can find one for both years that would be extremely helpful. Thanks

 

[Guest]

I believe I have a 1989 engine harness. The dash harness is 1991. If you have a pin diagram or know where I can find one for both years that would be extremely helpful. Thanks

this should help you if not let me know......

Ford Fuel Injection

 

[Nathandyke]

Thanks for all your help i know i haven't been back on in a while but that site ended up helping quite a bit. As it usually is a problem that completely stumps me usually ends of being either an oversight on my part or just something completely dumb. In this case it was both. In my hurry to complete the mustang before i moved I had accidently put the wrong computer back in my car. If anyone is curious the 4 cyl computer will not run a 5.0 engine duh. yeah when i figured out what I had done i felt pretty stupid. Anyways it is running great now and I'm loving the fact that after almost 3 yrs. I'm finally back behind the wheel of my mustang. Again thanks for the help. Nathan

 

[SimplyTwisted]

so you didn't need to make any harness changes? I am running into an issue running my 90 4cyl on a 89 5.0L harness. If anyone knows what pins I need to change please let me know. thanks.