86 is 2.3 carb to 5.0 carb swap underhood wiring info


New Member
Aug 26, 2018
Port Allen,La
Hello everyone, I'm new to stangnet and to mustang. I just recently inherited an 86 lx been in the family over 20 years body is solid and I want to bring this baby back to life .with that being said I want to make a respectable street car with say 300 hp. The cars a 5 speed I know that the 4cyl tranny and rear end will have to be upgraded to the v8 as well as the springs brakes sway bars spindles etc. My question is will the 4cyl underhood harness work at all or will I need to also change the underhood harness to the v8 harness . any help or info will be much appreciated thanks
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SN Certified Technician
Mar 10, 2000
Dublin GA

If you are an electrical dummy, you will need to either get smart real quick or find a suitable helper who is good with automotive electrical circuits & troubleshooting.

For free automotive electrical training, see Automotive Training and Resource Site . Once you are there, select online instruction. I have personally reviewed the material and it is very good. If you are new to automotive electrical troubleshooting, I highly recommend you spend a hour or so going through the material. You'll save at least that much time troubleshooting problems.

For straight up EFI: you will need the 5.0 EFI harness. If you want 300 HP, plan on doing a Mass Air Conversion. That will require a 89-93 5.0 Mustang computer and engine wiring harness.

MASS air conversion instructions from http://www.stangnet.com/tech/maf/massairconversion.html FREE

Revised 2 Aug 2014 to add new links to conversion harness suppliers, diagram for repining computer wiring connector and YouTube video

A9L (5 Speed) computer from junkyard $100-$150
A3M (5 Speed) computer from junkyard $100-$150
A9P (Auto or in a pinch, it will work in a 5 Speed car) computer from junkyard $100-$150
70MM MAF from 94-95 Mustang GT - $40-$70
MASS Air wiring harness kit $30-$85

The whole thing is probably less than $300 using junkyard parts.

A9L computers are 5 speed only
A9P computers are automatic, but will work with a 5 speed.

The conversion harness seems to work well for most folks. It avoids the compatibility problems in using a harness from the junkyard. Simple and cheap, actually less work that swapping the wiring harness.
Conversion Harness kits & parts

Youtube video how to do a Mass Air conversion using a conversion harness kit (somewhat long but useful)
View: http://www.youtube.com/watch?v=mnnTgXkHU9Q

Wire side 60 pin computer wiring harness connector

Computer side 60 pin computer wiring harness connector

If the idea of moving & soldering wires scares you, here's a list of compatible Mass Air wiring harnesses.

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.

Larger MAF to go with Mass Air conversion:
94-95 Mustang GT MAF - $40-$100. It is 70 MM instead of the stock 55 MM on regular stangs built prior to 94. It uses a slip on duct on the side that goes to the throttle body and a 4 bolt flange on the other. You need a flange adapter to fit the stock slip on air ducting that goes to the air box. Wiring plugs right in with no changes. *1 *2

*1.) Metal flange adapter http://www.kustomz.com/cat3.html Buy the TR70 for $40-$45 depending on if it’s on sale or not. Or spend some time on eBay looking for one that may fit.
Try AutoZone and ask for 81413 - Spectre / 3 in. Aluminum Intake Mass Air Flow Sensor Adapter at $12.00. You may have to order it online.

*2.) MAF & sensor interchange
The 94-95 Mustang 5.0 MAF & sensor is also found on:
1995-94 Mustang 3.8L F2VF-12B579-A2A,
1994-92 Crown Victoria 4.6L F2VF-12B579-A2A,
1995-94 Mustang, Mustang Cobra 5.0L F2VF-12B579-A2A,
1994-92 Town Car 4.6L F2VF-12B579-A2A,
1994-92 Grand Marquis 4.6L F2VF-12B579-A2A,
Evidently the –A1A, -A2A, AA, etc. on the end of the part number is a minor variant that did not change the operating specs. You should be able to ignore it and have everything work good.

If you want to go carb, find the wiring diagrams for an 85 Mustang 5.0 and use them to guide you though the project.

No matter what pat you take ,you will need to read wiring diagrams and trace circuits.

EFI to carb swaps

Revised 10 Aug 2017 to add comment about using an intank fuel pump form an 85 5.0 Mustang

A word of warning on EFI to carb swaps: don’t expect to pass emissions in any state that does comprehensive smog inspections, because it won’t happen. Some states will not title or issue license plates to cars that have been converted from EFI to carb. Be aware that you are violating several Federal laws concerning the removal of pollution control equipment. If you operate the vehicle on public highways and get caught by state or federal law enforcement (doubtful, but possible) you could be subject to fines and imprisonment. You won't get any more power from a carb than you will from a properly maintained and tuned EFI system.

The following information is intended for informational purposes only. Operation of a motor vehicle modified in such as manner as described below should be limited to off road use only.

Doing the swap; you must know how to read electrical diagrams and wire circuits to properly do the swap. Don’t take shortcuts or cut corners in the fabrication of the electrical or mechanical assemblies. If you do NASCAR quality work, the car will look good, run good and be as reliable as a carb’d car can be. Take pride in a job done with excellence.

If you are one of those few people who do excellent work, please disregard my negative comments. They are not intended for you.

Quality, quality, quality…
Some of the motivation of my negative comments about EFI to carb has to do with the quality of electrical workmanship. A lot of the wiring “repairs” that I have seen on the road and in the junkyard looks like road kill. The other part of my negative view stems from people who can’t grasp the operation and tuning of EFI. Carbs have their own set of requirements and some learning is required to get the best performance. Every car is different and each installation needs to be tuned to get the best performance. Putting an “out of the box carb” or one from someone else’s car isn’t the way to success. There is no auto compensation for small variations in carbs like there is for EFI. Just throwing a carb on a car because you won’t bother to learn how EFI works is a poor excuse.

Now that the rant is over, here’s some practical advice…

1. Do not use an EFI in tank fuel pump with a carb. You will never get the pressure/flow regulated properly. If the add on pressure regulator fails, you will flood the engine with gas and wash all the oil off the cylinder walls. That will cost you big time $$$. Either go full EFI or use a tank/fuel pump/fuel lines out of an 85 or earlier Stang. The in tank electric fuel pump from an 85 5.0 Stang can be used since it is only 10 PSI and not 40PSI+ output pressure that an EFI pump delivers.. Fabricating your own setup is possible but there are some snags to overcome.

2. Do not attempt to leave the EFI computer in place in an attempt to control either the electric fuel pump or ignition. Doing so qualifies you for the “Road Kill Mechanics Award”.

3. If you try to use your current tank, you will need to pull the fuel pump out and fabricate a pickup tube & strainer sock to replace the fuel pump. Or you can have a sump fabricated and welded onto you existing tank. Many welding shops will not weld fuel tanks because of the dangers involved if the tank isn't purged properly.

4. You will need an external electric fuel pump unless you change the timing cover for one with the mechanical fuel pump mount on it. The external pump will have to be mounted below the bottom of the tank to get the siphon effect needed to keep the pump fed sufficiently. Rip all the EFI wiring out, and the computer controlled fuel pump won't work. You will need to add a relay & switch and wire in the existing inertia switch for an external low pressure electric fuel pump. Do not try to wire the fuel pump without the relay. The 15-20 amps the pump pulls will overload the circuit. This will take power away from other items on the same circuit or cause the fuse or fuse link to blow.


6. You will need to run some new fuel feed lines or braided hose. The 3/8" aluminum tubing works well, but you will need a flaring tool and bending springs to fabricate the lines. Braided hose is easy to run and route, but is much more expensive. It is about $3.50-$4.00 a foot plus the end fittings, which are $3-$4 each. Fabricating hose assembles can be difficult, but anyplace that makes hydraulic hoses can do it for you for an extra charge. See http://www.amazonhose.com for more information.

7. For some help fabricating your own stainless steel hose assemblies, see
8. http://www.turbinefun.com/Stainless_Braided_Hose_Assembly.asp

9. For stainless steel braided hose and fittings for automotive use:

10. See http://www.summitracing.com/search/?keyword=stainless steel hose&dds=1
11. http://www.summitracing.com/search/?keyword=stainless steel hose&dds=1

12. http://www.jegs.com/webapp/wcs/stor...hall&searchTerm=stainless+steel+hose&x=18&y=4

13. See http://www.eaton.com/Eaton/Product...rformanceProducts/FittingsProducts/index.htm for more information on High performance automotive hose products

14. AN fittings require a 37 degree flaring tool. A standard automotive or household plumbing tool is 45 degrees and cannot be used with AN flare fittings. If you do, the flare is subjected to too much stress when the fitting is tightened, and is likely to fail or leak.

15. See http://www.mscdirect.com/ , http://www.mcmaster.com/ or for the flaring tool you will need . Prices start at $85 and go up

16. http://www1.mscdirect.com/CGI/N2DRVSH?PACACHE=000000013509163

18. http://www.mcmaster.com/#flaring-tools/=b4fxc3

20. Last time I was in Summit racing, they had a 37 degree flaring tool for less than $40. It may or may not be a catalog item.

21. While you are at the electrical part, you'll need a Duraspark or similar ignition system. The 85 Mustang GT 5 speed has a suitable Duraspark distributor with a steel gear compatible with the roller camshaft. The EFI ignition depends on the EFI sensors to advance the spark. Rip out the TPS and MAP/Baro sensors and the computer will have no idea of the proper ignition timing for best performance. Running a fixed timing setting is only for test purposes or for a race track only car. Don't try it on the street: the results will not be nearly as good as a properly setup Duraspark or equal. Crane makes a really nice distributor for non-EFI applications. . See http://www.cranecams.com/index.php?show=browseParts&lvl=4&prt=127 for more information. Cost is about $400, which makes the 85 Mustang reman units look really appealing.

Duraspark II ignition diagram:

Diagram courtesy of /www.billwrigley.com

See http://webpages.charter.net/1bad6t/duraspark.html for more help.
Note the ballast resistor shown in the diagram: you’ll need that too
If you use a coil from a 78 or later Mustang, you don't need the ballast resistor. The stock 89 Ford/Mustang ignition coil does not need a ballast resistor

A simpler HEI ignition that uses the same distributor and fewer parts can be found here. This is an excellent resource, and I suggest that you add it to your Internet Favorites

22. Tools needed:
23. Crimp tool for connector pins $9-$30 AutoZone, NAPA, Advance Auto Parts or other store
24. 100-150 watt soldering gun (recommend WELLER 8200PK soldering gun kit 100/140W) $30 at Lowes or $40 at Home Depot
25. 3/32”-1/8” rosin core electrical solder, 1/4 lb roll $6 at Ace Hardware, Home Depot or Lowes
26. Assorted sizes of heat shrink tubing. Buy long pieces and cut length to fit. It is cheaper that way. http://www.partsexpress.com/webpage.cfm?&WebPage_ID=346&CFID=169547&CFTOKEN=34300345
27. Hot air gun to shrink the tubing ($30-$40) Home Depot
28. Jeweler’s screwdriver kit $5 at Ace Hardware
29. Assorted automotive wire, 18-16 gauge 10’-20’ foot spools in different colors. $5 a roll at Advance Auto Parts.
30. Ford connector pins AutoZone, NAPA or other store $5-$10 for a kit of 10-12 assorted pins

31. You will have $110-$150 in materials and tools if you don't already have them.

32. The water temp and oil pressure signals feed from the sender to the main harness through the 10 pin EFI engine harness. To utilize these senders, you need to identify the wires and find a way to reconnect them to the main harness after the EFI engine harness is removed. You need a weatherproof quick connector to join the sender wiring to the main harness.

33. See the graphic for the 10 pin connector circuit layout.

34. The injector power pin is the VPWR pin in the black 10 pin connector.

35. You will need to construct a wiring harness from the ‘85 carb distributor to the Duraspark box if you go Duraspark, or other distributor to coil wiring.
36. The voltmeter picks up its signal from the switched voltage present on the instrument panel, so you don’t need to worry about that.

37. The fuel tank gauge is also independent of the computer wiring.

38. AutoZone wiring diagrams can be found if you are willing to dig through the self help repair section of their website. http://www.autozone.com/autozone/re...3835D6CFF5E3A5037BBBD332CF445FF.diyprod2-b2c3

39. How to solder - see
View: http://youtu.be/uaYdCRjDr4A
This is an excellent how to do it.

40. Soldering pigtails onto existing pins is road kill quality work as far as I am concerned. Take some time to study the way the Ford connectors are assembled and you will find that a small jeweler’s screwdriver will release the pins from the connector shell. New pins and a crimping tool are available from the Standard Motor Parts or Bendix Electrical parts line that the NAPA & Bumper to Bumper Auto Parts stores carry. Ask any auto parts store about Standard Motor Products or Bendix Electrical wiring parts. Those that carry them will be able to get the parts you need. AutoZone has a cheap kit with 10 pins for about $5. Just enough pins to leave you short when assembling a connector.

41. One of the interesting things about the Ford OEM wiring diagrams is that the connector shape on the drawing matches the connector shape in the car. That makes it easier to identify connectors and circuits. OEM Ford diagrams are available at for an 85 Mustang at http://www.helminc.com/helm/Result....edia=&mscsid=2M838NG3R5SR2MCS00A3HVE05T03C501 or can be found in the Chilton series of auto repair manuals for Mustangs.

42. The following is an excellent idea from a fellow Stangnetter who tackled the wiring plan the right way. He obtained the wiring diagrams from an 85 carb'd V8 Mustang and laid them out side by side with the diagrams from his car. He then traced out each circuit and the wire colors and connectors associated with them. After tracing the circuit and connectors for a circuit, he laid out the changes he needed to make. One circuit at a time made a difficult big job into many smaller easy to manage jobs.

43. Copied from pikapp33.
JR’s comments:
I have heard that there have been quality problems with some of these Richporter distributors, but that may be a limited quantity of the units.

I recently changed my EFI mustang back to carb with MSD ignition, to save some money and go for a more simplistic approach. I researched, and found the best stock type distributor to use was from an 83 Bronco 5.0, which is a Duraspark (magnetic pickup, same as what MSD dists use), making it possible to use the 2 wire MSD trigger input, and also has a steel gear to work with the EFI hydraulic roller cam.

I chose to use a Richporter FD30 ($85). Then added a BWD C194A Cap Adapter ($12) to use the Fox style dist cap/wires (the Richporter comes with cap/rotor, which I didn't use; other brands come without and are cheaper, but have a core as well; no core on this one). And then a BWD D166 rotor ($6) to match the cap adapter. I also chose to buy the MSD 8869 adapter wire ($20ish) to connect the dist to the MSD harness for my 6AL. All together about $125, much cheaper than the MSD billet dists, and am very happy with the quality of the dist and the way the setup worked out.

The Richporter FD30 distributor is available at Advance Auto Parts ($90) & O’Riley’s ($81)


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