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Discussion Starter #1
Im switching over my friends 88 from speed density to mass air. I scored a 1990 wiring harness complete with A9L computer and fuel injector harness and O2 wiring harness. I was told I needed a 89 harness and computer because of a few differences with the 89 and 90 harnesses. Is that True? and can I make a 1990 harness work with this 88 or would I be better off sending it back and looking for a 89? This harness is as complete as they come. it even had the stock grommet that goes through the fire wall. with that being said, im not sure why I couldnt use it. Please help, I have to the end of the day to let this guy know if I want it or not. this is the link to a picture of what I bought.
A9L Computer and Wiring Harness 1990 Ford Mustang EEC IV | eBay
 

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I have an 88 Gt hatch, years ago I bought a kit from e-bay, and added it to my 88 harness, got a meter and an A9L computer, and it worked great for years.

I found thru searching, for a direct swap you need an 89 mas harness the grey and and black barrel plugs into the dash plugs, is what makes the diff,


on my conversion I added the wire, and pinned it in the computer main plug.
now i have my engine out, swapping to a 89 mas harness, tucking wires, painting the bay, I got that harness for sale pretty cheap if you wanna look at it, use it with all your meter an computer, would work. its in electronics
 

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do a search here.

harnesses are year specific. they are not plug and play.

they can be made to work, its just wire and pin locations.

is it worth it?, its up to you.

the dash and engine harness will NOT interface with your combo without modification.
 

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Much easier to use your existing harness than swap them around. In the end, nobody will know the difference, so why spend all that extra time?
 

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Discussion Starter #5
I've seen lots if kits to use your existing harness but I'm just not sure what kit I need anybody or a link to exactly what I need?
 

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You need the comp., a MAF sensor. The maf sensor harness that gets run from the maf to the computer, (should come with eec pins) swap 2 thermactor pins around in the plug, you need 3 extra EEC pins and run 3 wires over from the drivers side and tie those into the comp. as well.

(obviously there's more to it, but that's the basics)
 

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Discussion Starter #9 (Edited)
You need the comp., a MAF sensor. The maf sensor harness that gets run from the maf to the computer, (should come with eec pins) swap 2 thermactor pins around in the plug, you need 3 extra EEC pins and run 3 wires over from the drivers side and tie those into the comp. as well.

(obviously there's more to it, but that's the basics)
So if I follow these instructions on this link, and use the connector, I should be good right?
Mass Air Conversion Harness - Wiring & Accessories
 

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Oh ya, i might still have my stock mass air flow meter laying around in my garage some where, if you need it, you can have it, if you pay the shipping on it. I mean its just stock but it might get you by until you want to upgrade.
 

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Discussion Starter #13
I got a 1990 A9L computer. That should work with the 88 after the harness is re pinned right?
 

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due to the conversion by Ford to MAF for CA cars, there are two different configurations of O2 sensor wiring harnesses used in 87-88 cars. One set uses a 5 wire configuration and one uses an 8 wire confiruration. If you have the 8 wire configuration a wiring conversion kit will work well for you to keep the O2 sensors working correctly - just did this on my late 87 built 88 GT. Check the O2 connectors and count the number of wires in them. Other than that, you need to use an 89 harness. Rewiring the 90 harness to work is not worth it imho.
 

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I used an A9L also, one thing not mentioned yet, I did my conversion, I pulled that big rubber plug, where the harness comes thru the fire wall, and ran the new cable thru there, That was a mistake I never did get the firewall sealed back correctly, so if you go that way, it'd be better to run it thru the fender, maybe drill a hole, big enough to put a rubber grommet around it in the hole.

I was going to fix mine, but I'm just going to tuck an 89 harness in there right, Good luck with it.
 

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Discussion Starter #17
I used an A9L also, one thing not mentioned yet, I did my conversion, I pulled that big rubber plug, where the harness comes thru the fire wall, and ran the new cable thru there, That was a mistake I never did get the firewall sealed back correctly, so if you go that way, it'd be better to run it thru the fender, maybe drill a hole, big enough to put a rubber grommet around it in the hole.

I was going to fix mine, but I'm just going to tuck an 89 harness in there right, Good luck with it.
How many wires do you have to run through the firewall to the computer?
 

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How many wires do you have to run through the firewall to the computer?
just the one cable with the wires in it for the maf plug, if you can see the pic its that wire in the middle
 

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Discussion Starter #19
Ok I got it. I think I got a pretty good handle on this now. I'm just waiting on him to get the rest of the parts together
 

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OK, I am going to post some info I found to be good - with the caveat that he says an 87 O2 harness is not an 8 wire - My car was built in late 87 and it had the 8 wire O2 sensor harness, so keep in mind if you have an 87-88 car that you must check the cannon plugs and count the wires - here you go........

87-88. Lets start here. The 87 mustang fox body 5.0 cars were pure speed density cars. This is the second year of the EFI fuel injection system and the complete make over from the 86 style interior and exterior. Some features of the speed density harness are the 2 cannon plugs near brake booster. One should be gray and the other is black. What I mean by "near the brake booster" means where that part of the harness would sit if installed. Also another feature of a pure speed density harness is there’s no provision for a mass air meter plug. Basically this would be located near the 02 harness cannon plug as well as the wide open throttle (WOT) AC cutoff relay. So just looking at those 2 things can pretty much tell you what kind of harness this is. Now moving on, in 1988 there threw a monkey wrench in the mix with the engine harness. Now an 88 harness will work just fine in a speed density 87 OR 88 car no problems with the DC or the DA1 speed density computers. However 1988 was the first year for emissions in California so pending on what the production date was for that 88 mustang harness depends on whether the harness got the extra plumbing provisions for the 02 harness. This will also effect whether the harness can be converted to mass air or not too.

02 Harness plugs. 1987 if you look at the backside of the female 02 harness cannon plug that is found on the MAIN HARNESS (not the 02 harness itself) you will see 5 wires. The cannon plug I'm talking about is the actual plug that the 02 harness PLUG INTO aka the female part. Since 1988 was the FIRST year for the mass air harness for cars sold in CALIFORNIA only, your 1988 car can actually already be equipped with the 8 wire 02 female cannon plug found in all mass air cars but still be speed density. It will work just fine. What’s all this mean? 5 wire 1987 harnesses can NOT be converted to mass air by just running the 4 wires, changing computers and moving the other 2 wires as found in many write ups. Why? Because 1987 didn’t have the proper plumbing for the 02 harness signal return that the mass air computer needs. Also the 02 harness didn’t have the jumper loop to provision this change found in all mass air cars. Let’s put this in a situational basis. You have an 87 and wanted to convert to mass air. Well forget about it. Either buy an 88 speed density harness with the 8 wire 02 plug or buy an 89 mass air engine harness. Because all 89 5.0 cars came equipped mass air. If you wanted to convert your 88 to mass air engine harness you would have to first check to see how many wires are on your female cannon plug on the engine harness. If there are 8 you can proceed as normal. If there are 5 then forget about it. Just get an 89 mass air harness. Sure you could spend the time to plumb the other 3 02 harness wires but it’s more of a pain than you think. IF YOUR GOING TO CONVERT TO MASS AIR MAKE SURE YOU CHANGE THE 02 HARNESS WITH THE ENGINE HARNESS AS WELL. JUST RUNNING 4 WIRES AND A METER ISNT EVEN THE HALF OF IT. CONFUSED YET? LOL

The 1989 Mass Air Harness. Simply put, in 1989 all 5.0 cars were converted to mass air harness. This was the same exact harness that could be easily used in 1987 and 1988 cars with no issues. This harness can NOT BE USED in any cars past 1989. Just 87-89 ONLY. It’s simple to identify. Of course it had the natural gray and black cannon plugs near the brake booster. It has the oval mass air plug near the WOT AC cut off relay and 02 harness female connector found on the passenger side inner fender skirt apron. It also has the 8 pin female 02 harness plug and now came with the jumper looped 02 harness for that specific transmission signal return. What’s a signal return? Well it’s just that, it’s a jumper loop monitor wire that is solid purple with a yellow stripe on it. If you take your 02 harness apart from the engine harness and peel it back about 2 inches you will see it will "loop" back to the cannon plug and return to the ECU that way. Not having the proper 02 harness for the ECU that’s installed and specific transmission in the car can lead to BIG problems with the ECU including frying a trace inside the ECU. It will also be a TUNING NIGHTMARE as most tuners won’t even get the 02 harness to communicate with their tuner programs, data log or anything.

The 1990 Mass Air Harness. Well this year started some big changes to the fox mustang. We are lucky to even have 1990-1993 fox mustang as they were almost replaced by the failure of a car the FORD PROBE. So naturally they did some changes to the cars interior. The exterior pretty much was identical but the engine harnesses were NOT. 1990 engine harness started the provision for the air bags. So they moved some wires in those two cannon plugs near the brake booster. The gray and black plugs that are found in 87-89's that we spoke of previously. So with that being said, this will only work in 1990's mustangs exclusively. It will NOT work in 87-89 or 91-93. What a pain in the arse right? Well at least I’m taking the time to write this for you, so you can only blame yourself when you buy the wrong harness and see it not work right. It will also plug and play with all 4cyl swap cars that were equipped with 1990 original equipment i.e. the dash harness ETC.

The 1991 Mass Air Harness. Well guess what folks, they changed the harness AGAIN!!!!!!!!!! Yep, 1991 will ONLY WORK WITH 1991. What’s the biggest feature differences in 1991 compared to the others? Easy. Remember that gray and black 8 pin cannon plugs near the brake booster? There’s only 1 plug there now. And it’s brown. The black plug moved to the ECU side of the harness, it can be found down near the ECU. Also as the 89 and 90 had in their harnesses, of course the 91 had the oval mass air plug on the passenger side fender apron. The big brown cannon plug found near the brake booster was the same in 92 and 93 as well. However how would I tell the difference between 91, 92 and 93 then? Easy again... and I will get to it. Basically if you have a mustang engine harness that has 1 big brown plug near the brake booster and black plug near ECU then it’s either 91-93. Now to tell the difference between the 91, 92 and 93 go look at the passenger side fender apron part of the harness. In 1991 there will only be the oval mass air plug, the WOT AC shut off relay, the white cannon plug for air bag passenger side and finally the large 8 pin 02 female connector for the 02 harness. That’s all..... if there’s an extra relay there... it’s not a 1991 harness..... moving on..

The 1992-1993 Mass Air Harness. Well finally got to the end of the line. Simply put 1992 and 1993 harnesses will work together no problems. None of the previous harnesses will work at all. The reason being is because of one major change in the harness and car itself. Basically the 1992 and 1993 harnesses are the same as the 1991 harness with one added feature. The passenger side apron of the harness got ANOTHER relay. This is the fuel pump relay. So how do you tell if you have a 92-93 harness? Just look at the passenger side apron and you should have the following: Oval mass air plug, white cannon plug (4 pin) for air bag, Large 8 pin female connector for 02 harness, WOT AC shut off relay, and finally the new provision being the fuel pump relay itself was moved here too... Usually has a "white" cap on the relay. So the plug isn’t all black like the AC shut off relay. 91 was the last year they had fuel pump relays under the driver’s seat. They were moved to this location in all the engine harness's 92-93.
 
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