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5-spd Mustangs do not use a Nuetral Safety switch. They use a clutch safety switch. This is the black plug that has the jumper in it under the dash. Remove the jumper, and plug this into your clutch switch.

AOD mustangs DO use a neutral safety switch. The two wires that make up this neutral safety are part of the 4-wire plug that makes up the reverse harness. On the T-5, it's jumped out under the car.
1072004

You can see on the harness the red loop? That's where the Nuetral Safety is jumped on a 5-spd. You need this jumper AND the plug plugged into the clutch switch to complete the proper starting circuit for the 5-spd.

Now, about the other plug under the dash and the plug on the top of the T5? That's the NGS. Nuetral Gear Switch. It's only purpose is to tell the ECU that the trans is in neutral. The clear one under the dash, you can just plug that in.

However, you don't have the one on top of the T5 since you are using a SN95 t5. You can swap the top cover from a Fox to one with it if you'd like, or you can just live with it. One thing to point out however is that AOD cars do NOT have the provision for the NGS plug on the T5 in the transmission harness. This is the harness from the driver's kick panel under the seat, and out to the trans tunnel. You'll need to swap the harness, or run 2 wired from the NGS to the kick-panel inside and tie into the body harness.

When I did my 5-spd swap, I forgot the little pin under the NGS on the T5. Found it days later on my bench and had a "Dammit, I forgot to put that in moment". I was't dropping the trans again so I decided to let it go. I changed all the other wiring, plugged in the two plugs on the clutch switch and the car was a driving 5-spd. What I found was that I would get idle hanging issues if I shifted to neutral and let the clutch out and came to a stop. The idle would hang up around 1200RPM or so, until I pressed in the clutch and then it would settle down to idle and be fine. I just lived with it. To run the codes, I would just run them with the clutch pedal pushed in. One day I finally got around to installing the pin under the NGS, and this issue no longer occurred.

In the past, I have recommended to some that they just put a 5A blade fuse in the clear NGS plug to keep it jumped out all the time. This would solve the idle hang issue, but I do not know what consequences are in terms of timing/fuel/etc within the ECU when it thinks it is in neutral.

In general, i'm a big supporter of the "Do it right" methodology in which all the harnesses and such are as close to factory as possible so that the ECU is as happy as it can be in terms of how it runs the car. For a AOD-to-5spd swap, that does mean changing the trans harness and having both NGS switches connected, as well as changing out the AOD ECU to a manual ECU. This also means you will need to check and possibly change the jumper on the O2 harness to a 5-spd jumper position as well.
 
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Thank you so much for the speedy reply! You are a life saver! So pretty much I have a few options. First I can change the harness to a proper t5 harness and change the top cover of the t5 to incorporate the NGS. Regardless the black connector that is jumped under the dash needs to get plugged in regardless of what I decide to do. I can plug both the black and clear connectors into the clutch safety switch, this will allow me to start the car only when the clutch is engaged but will leave me with idle hanging issues. And lastly, I could plug the black connector into the clutch pedal assembly and throw a fuse into the clear connector. Doing this will stop the idle hanging issues but would leave me with the ability to crank the motor in any gear. Is that correct? And thanks again.

The correct, factory OEM way to do this is like this. This includes swapping the ECU to a proper 5-spd ECU and also assumes this is a factory mass air car. This also assumes factory harnesses are already installed

Plug both plugs (black and clear) into the clutch pedal switch
Replace AOD transmission harness with manual trans harness listed above
connect NGS on top of T5
Install t5 reverse harness (which contains the red NSS jumper shown above)

The above is plug and play. No guesswork or wiring diagrams needed and pretty straightforward. Now, if you did want to save a few bucks, you could just buy the NGS plug and run 2 wires to the driver's kick panel. You'll need to find the proper wire colors to hook to for this, but it will save you from having to buy the manual trans harness. You would need to track down the proper two wires in the driver's kick panel to tie into.

Now the most important part. The O2 harness jumper. Since yours is a converted 4cyl, this is especially critical for you, and i'm sure you've seen this mentioned before. The harnesses need to match the year and ECU and trans in the car. The jumper needs to be changed accordingly when you swapping ECUs (or putting a 4cyl conversion together from mixed harnesses).

Simplified, if this was a factory 5.0 with factory installed harnesses and originally an AOD, you would swap the jumper appropriately, test pin 46 for voltage, and then install the 5-spd ECU and crank the car up. With it being a former 4cyl, you'l want to do more due diligence that your harnesses are correct and verify against wiring diagrams, otherwise you risk damaging your ECU. This is very important.

Now, I know a few people will read this and think "That's BS you don't need to do any of that". That may be true, and the car will run and drive, but the above will ensure the car runs properly. No hanging idles, properly working safety wiring, and ability to run/dump codes without needing to jump out certain things.


My car was a speed density AOD and is now a 5-spd Mass Air car, so i'm speaking of this all from experience.
 

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The clear one has nothing to do with the starter circuit.

Black is starter circuit. This one must be plugged in so the car will start when you press the clutch pedal in

Clear indicates to the ECU that trans is in nuetral or clutch pedal is pressed in. You are jumping this one temporarily, but is has nothing to do with nuetral safety or interrupting the starter circuit.

I do not know the detrimental effects of the ECU always thinking it’s in “neutral” with it jumped it.

I am also not sure what greyplug in the drivers kick panel you are talking about?
 

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Mustang5L5 -- The LMR harness (that you referenced in an above post) says it's for an 87-93. I am planning a T-5 swap into a 1986 GT with an AOD. Will this harness work with my 86 application? Anything else different with the 86 vs 87 and up? Thanks!
So i must admit, i am much better with 87-93 wiring than pre-87 wiring. I do have an 86 EVTM so I can check this out later on.

I want to say that in this particular case the main difference is the connectors. I know this is true with 1985 wiring as it has a lot of unique 1-year connectors, but i'm not 100% sure on 1986. I'll dig into it later on when i can check out the '86 EVTM.


That particular harness (at least the 87-93 version) carries three circuits. 2 wires for the VSS. 2 wires for the backup light and 2 wires for the neutral safety which is only used on AOD cars. On the 5-spd cars the NSS is just jumpered out on the red/blue wire on post 2 and Ford relied on a clutch safety to prevent you from starting in gear.

I'll have to check later to see if the 86 cars are wired similarly, but I want to say they are and it's a connector mismatch. Sorry i can't give a more definitive answer just yet.
 

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Ok, looks like ford still routed the three circuits through the same harness like the 87-93 cars, but the location of the plug is different. It comes up the trans tunnel and connects center of the dash behind the center of the instrument panel(th is might mean dash) , not the kick panel.

black 8-pin plug, C350 on the wiring diagrams . Cannot locate a diagram showing the location.

for wire colors:

VSS: black/white stripe, Dark Green/white stripe
Backup lights: purple/orange stripe, black/pink stripe
Neutral safety: white/pink, red/lt blue

Unsure if the other two spots on the 8-pin connector are occupied, so possibly 6 wires in a black 8-pin connector. See if you can locate it under the dash. I’ll update if I find more info

still unknown if the 87-93 harness would work. Would need to see the 86 harness first
 
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How many wires are in that plug and what are the colors?

I see more than 6. Possible you already have the connection for the NGS?
 

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I forgot a circuit.

So should be 8 wires.

2 for backup
2 for VSS

those match the EVTM.

the wire colors for the VSS don’t match up. There’s two for those. Then there should be 2 for the NGS on top of the t5. I can’t find those wire colors in the EVTM, but Ford did a terrible job diagramming that out on the 87-93 cars as well and the EVTM is actually incorrect.

anyway, it’s possible since your have 8 wires in that plug, that you might already have the plug for the NGS present. Have you gone under the car and verified if it is in fact there? My 88 aod car only had 6 wires in the harness so I had to swap to the 8-wire manual harness, but it looks like yours might not need to be changed.

ultimately that’s what drove us on this hunt right? Adding the correct harness for the NGS?
 

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It’s also entirely possible that it’s not used the same way as the 87+ cars. The more I look through the EVTM the more differences I spot. Like I said, I’m pretty good with 87-93 wiring but pre-87 stuff I’m still just figuring it out along with the rest of you.

I will say though that Ford improved how it wrote the EVTMs as the years went on.
 

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The 5-spd cars bypass the NSS that is normally used on the AOD cars. It gets jumped out on the reverse harness pigtail. Red wire with blue stripe.

the connector on top of the T5 is called the NGS or nuetral gear switch. It’s not a nuetral safety. The 5-spd cars rely on a clutch starter safety switch and those plugs are tucked under the dash over near where the clutch pedal hangs. Just need to remove the jumper and plug them in.

the NGS May affect idle quality and cause a hanging idle on “some” cars if left disconnected. My car had this issue which was cured by plugging in the NGS. Other cars run perfectly fine without it.

since I’m all about keeping wiring and such as close to OE correct with little variation, I recommend putting in the effort to see what it would take to hook it up proper. I also typically recommend using a 5-spd ECU. Again some folks never have an issue with the aod stuff, but I did. I left the NGS unhooked and ran the aod ECU. Every once in a while I had hanging idle issues that I could never solve. Finally I swapped to the correct 5-spd wiring first and then an A9L and all that went away and the car has never run better.
 

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See attached picture. Does this harness look like the NSS harness that I need to install for my T5 transmission (which replaces the existing AOD harness that is running to through the trans tunnel)? I don't have a wiring diagram for the harness.
View attachment 1092605

Here is the wire identification for the above harness

Rev = Reverse light switch
NSS = Nuetral safety jumper
VSS = speed sensor
NGS = Nuetral gear switch (top of T5)

Asphalt Road surface Gas Composite material Wire
 

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Thanks for the harness identification!

Here is a checklist of what I think I need to do from a wiring perspective to get the T5 to function properly in the 86 Mustang with speed density which formerly had an AOD, but am not experienced/knowledgeable enough to know if it is correct -- what am I missing? Assume the T5 trans, pedals, etc... are fully installed.

1. Replace AOD harness with a T5 harness (like in the picture). This assumes I have the correct T5 harness which I will need to verify.
2. Obtain a NGS (and install in the T5) and hook up the NGS connector in the T5 harness to the T5 Transmission.
3. Hook up VSS and Reverse connectors.
4. Find the connections for the starter clutch pedal switch & NSS, and plug them into the clutch pedal switch assembly.
5. Hook up the cruise control switch connector to the clutch pedal.
6. No need to touch the 02 harness with A9P or A9L if keeping speed density.
7. If using an A9P computer, there might be issues like hanging idle. But if using an A9L computer, there should be no hanging idle issues. Note: I currently have a used A9P that I could try out, but I don't have an A9L.

you only need to do 1 and 2 if you are changing out from the AOD ecu to the 5-spd ECU.

Both AOD and 5-spd cars use the same VSS and such, so this should be an easy swap. 86-88 cars use the VSS only for cruise control. Mass air cars do have an ECU connection to the VSS so the wires need to be added to pin 3 and 6 when you do a MA conversion

For step 5, the wire should be present with a jumper on it clipped to the metal support bracket near the gas pedal. Just remove the jumper and plug into the cruise disconnect plug on the pedal assemble. I recommend making sure all the cruise components are present and properly installed before installing the pedal assembly.

For 6, the o2 sensor harness jumper is a 1988+ thing. It's not present on 1987 and from what I can see also not present on 1986.

Unknown for #7 regarding the A9P. It might hang, it might not. I found it did with the A9L until i hooked up the NGS on the T5 and the only really mine wasn't hooked up was because I missed up and forgot to install the little pin under the detent ball. I wasn' dropping the trans to install that without a better reason, so I lived with it. It did it infrequently enough that it didn't bother me. Adding the pin cured it completely.


I would simplify things a lot here. Disregard the MA swap for now.

You can keep your current ECU and just hook up the clutch starter interrupt switch and the clutch NGS, and hook up the reverse light and VSS (if equipped). That will get you a running and driving 5-spd car. This will get you up and running with minimal hassle. Might you get a hanging idle from time to time? Maybe. I did.

Now, to do it factory OE correct, you'll want to track down a 5-spd 1986 speed density manual ecu. Unknown if 87 and 88 can be used. 1986 won't have the O2 sensor harness jumper. From what i see in the EVTM, it's similar to 1987 is that there is no difference in how the autos and manuals are wired for pin 30. Swap that in, install the correct trans harness that has the provision for the NGS (or run 2 wires) and that's really all that's needed.

Later on, if you want to mass air swap. Use an A9L or other 5-spd ECU, repin for the MA, and add 2 wire for the VSS (pin 3 and 6 i believe) and the single wire for the fuel pump monitor.
 

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This is where you do need the manual. Kinda need to get in the car and trace things out and verify colors on the EVTM.

It’s clear to me there are enough differences in how 86 routed the wires vs 87+ that I shouldn’t make assumptions on how a circuit runs.
 

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Mine is an ‘88. I swapped it to a 5-spd and then later mass air (A9L)

I just plugged it all in. Nothing else really needed.

when I did my MA swap I went from AOD SD ECU to the 5-spd MA ECU. I had to change the o2 sensor harness jumper, but like I said, that’s an 88+ issue.
 

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BTW, I am amazed at how differently and poorly written the wiring diagrams are for the 86 mustang -- but I was able to piece the wiring together!
Yeah, they get even worse the further you go back.


They get progressively better each year peaking in 1992 with more pages added. The 93 one was extensively redrawn and omits a lot of the details like wiring harness diagrams and identification.
 
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