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I'm trying to figure out which wire to putt on ACC. I have a

I'm trying to figure out...
I'm trying to figure out which wire to putt on ACC. I have a 75 Bronco with a 1990 5.0 motor. I just put in a 3G alternator and removed my condensor and voltage regulator. When I turn off the key my motor keeps running. I'm trying to figure out what wire I need to put on ACC so that I can shut down my motor. Right now the computer is tied into the Bronco electronics with two wires that got the positive side of the starter solenoid. One is 20 amp fused and the other 25 amp fused. Bot***** *****ne is that I can't turn my motor off once it starts. I figure there is something I need to connect to ACC so that my ignition will kill the power.
JA: Is the car in "Park" or "Neutral?" Do you know if your car has a "wheel lock" feature?
Customer: Not relevant, no neutral switch, but good question. 1975 Bronco.
JA: Are you fixing your Bronco yourself? What have you tried so far?
Customer: Yes.
JA: Anything else you want the mechanic to know before I connect you?
Customer: I upgraded to a 3G alternator from the old 38amp model that used a condenser and regulator. I did the following..
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Answered in 17 minutes by:
9/13/2017
Jared D
Jared D, ASE Certified Technician
Category: Ford
Satisfied Customers: 1,983
Experience: Shop Supervisor at County Fleet
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Good afternoon,

It's hard to picture what you have exactly, but it sounds like the alternator is back feeding the ignition circuit. What terminals do you have connected on the back of the alternator?

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Customer reply replied 2 months ago
Good, I can add some detail here. I got a 130 amp 3g alternator to put in my Bronco. It is internally regulated, so I no longer needed my condenser or voltage regulator. The alternator came with a pig tail on top with two wires. A white wire and a reddish orange wire. I also bought a heavy duty cable to connect the alternator battery connection to the positive side of the starter solenoid. From the pigtail on the alternator, the red wire connected to the same place as the battery connection. The lone white wire was then to be connected to the orange wire that ran to the voltage regulator. The orange wire is spliced to a green/red wire that heads into the firewall. ----- The original wiring to the regulator included 4 wires. 1 orange. 1 green red. 1 yellow that was a pigtail. There was also a ground in there. Basically I removed all the wiring, traced them back, removed what I wasn't using, spliced together the orange and the red/green that connects to the alternator white. The remaining two heavy wires originally went to two places. The fused link went to the positive of the starter solenoid, and the other wire went to the back of the alternator's battery link. ------- This is a 1975 Bronco. It has a 1990 5.0 motor in it. The computer for the mustang is wired in with two fused links going to the positive side of the starter solenoid. At this point, I think my solution is to leave everything connected as is, and find some wire in the harness that needs to be connected to the ignition ACC/ON switch. As it is, once I start, the key does not stop the truck, unless I disconnect the coil wire.
Customer reply replied 2 months ago
I have heard the term back-feeding. The additional writing I just provided may help. I also have a couple photos that may help if you like.

Ok. So check to see if you are getting 12 volts to the distributor ignition wire all the time. This wire should only get voltage in the run position and voltage should cut out in the off or accessory position.

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Customer reply replied 2 months ago
Ok, in testing I have done the following. My knee jerk reaction when the truck would not shut off initially was to just disconnect the negative post of the battery. The truck kept running. I then pulled the S and I terminals off the starter solenoid, still running. I had already tested that I get power to the alternator through the orange wire that gets spliced to the white alternator wire. The final thing I did to shut off the truck was to cut the orange wire that goes to the white wire, and still the engine kept running.With the key in the RUN position, I do get power to the orange wire as I recall. Everything worked fine before this upgrade by the way. Also with the key in RUN position, I don't believe I was getting power at either wire going into the coil either.
IMG_1221.JPGIMG_1221.JPGIMG_1429.JPGIMG_1429.JPGIMG_1222.JPGIMG_1222.JPGIMG_1431.JPGIMG_1431.JPGIMG_1434.JPGIMG_1434.JPGIMG_1458.JPGIMG_1458.JPGIMG_1460.JPGIMG_1460.JPG
Customer reply replied 2 months ago
Now whether that as truly 12v, possibly not, but the tester light I was using lit up each and every time very bright and strong just like it had on the battery terminal.
Customer reply replied 2 months ago
correct on the orange wire question. Hot to the alternator while in RUN position. Off when key off.
Customer reply replied 2 months ago
I am at the 88-91 Mustang wiring schematic. I think I need to identify a hot wire that I need to attach to ACC/RUN positions so it turns off with the battery. I'll send over the schematic.
Customer reply replied 2 months ago
Give up?
I'm sorry. I was having internet issues at the shop. I will look at the wiring diagrams and see if I can figure out how it's back feeding. I'm using my cell to respond now, but I should be able to respond from home later this evening.
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Customer reply replied 2 months ago
Great, thanks. If it is indeed "back feeding," have you heard of a Zenner or Axial Diode? Alternator people guessed that as an option. It in some way only allows electricity to flow one way? That was his thought... until we cut the ignition wire going to the alternator and it still kept running, then he changed his mind. But that is how I heard the term before. I'm just out of guesses.
Customer reply replied 2 months ago
I did start a thread on a website to get input. It might help you get another look at it including photos.http://classicbroncos.com/forums/showthread.php?p=3008595#post3008595
Customer reply replied 2 months ago
I'm suspicious of the two wires that I'm unsure of. There was a white wire coming off the original alternator that was never hooked up. I didn't disconnect it and never knew its function, but things ran without it, so I never addressed it. Perhaps it was cut out for a reason to allow the 5.0 to work properly. I didn't install the 5.0 wiring. The other wire is the yellow wire that pig tailed into the regulator. It went back to the fused link black wire that goes to the solenoid. I just clipped it. There was a final ground that ran into a block of rubber. It seemed to ground the block of rubber more than anything. I was really corroded and didn't appear to function. It had no where to go. I think it originated on the firewall above the condenser.

Try disconnecting the light green with red wire in the diagram I sent while running and see if it shuts off.

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Customer reply replied 2 months ago
To answer your first question. If I disconnect the orange wire or the white wire that goes to the alternator while the engine is running with the key in the off position, the engine keeps running. I can't disconnect both of the red and white wire at the same time with the engine running because the plug that goes into the alternator is right up against the bracket that holds the alternator. But yes, if I disconnect the orange wire while the engine is running with the off position, the trek continues to run. I'll take a look at that other drawing. I'll get back to you.
Customer reply replied 2 months ago
I looked at the drawings, that is not but the back of my alternator looks like. I'll see if I can send you a picture of the back of the new alternator, as well as where I purchased it from. There is a description there. I can also give you the phone number of the people that I bought The alternator from, because they are the one that think it works in a Bronco like mine.https://m.ebay.com/itm/66-77-EARLY-CLASSIC-FORD-BRONCO-3-WIRE-ALTERNATOR-135-A-/130256557920?txnId=1384492198003
Customer reply replied 2 months ago
This is the guys phone number I've been talking to. He may recognize my name Lawson. He and I talked about it this weekend. Perhaps he knows something. He claims to have 40 years experience. I'm just the monkey that connects the wires. :-)+1(###) ###-####
Customer reply replied 2 months ago
I don't think I clarified. He is the one I purchased the alternator from. He is the one that claims that it works at 66 through 77 bronco. He is the one that calls it a 3G alternator.

That looks very similar to the GM style "one-wire" alternator. Did it come with any wiring instructions?

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Customer reply replied 2 months ago
I wired it while talking to the gentleman. The it is a GM style alternator. The red wire goes to the battery plus the battery plus then goes to the starter solenoid plus, and the white wire goes back to the original equipment orange wire. I think a call to him might be fruitful. He can explain things like fields and things of that nature That I have no clue about.
Customer reply replied 2 months ago
That is a cell phone number for him, so you could text him.

I'm running the same alternator on my Chevelle. I just installed and wired it last week.

Ok, maybe that's not where it's back feeding. If it was the engine should shut off when you disconnect the white wire since that's the only feed on the alternator where it could back feed. What else do you have connected to the ignition solenoid post? If you have it hooked up like this (pardon my drawing skills). Then the alternator doesn't seem to be the source of the backfeed (as long as disconnecting the white wire doesn't shut the engine off when the key is in the off position).

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Customer reply replied 2 months ago
Well, I have two views the wires that go to the starter side of the Sillen Noyd that power the computer system for the 5.0. And yes you are correct if I disconnect the white wire the engine continues to run even if the key in the off position. The only thing that I can think to do is to find a wire that comes off the computer harness that I can attach to the ignition source, rather than some hot sores that I may possibly be bringing into the computer. I could look closely and figure out where those two wires come into the computer from the battery, but basically it is to fused wires want to 20 A and one and 25 A. I recall seeing a drawing at one point that shows that those are how the computer is typically powered. So basically when the people put the wiring into the bronco for me, they just took those two lines the 20 and 25 amp lines and connected them to the positive side of the solenoid.
Customer reply replied 2 months ago
I have two fused wires, not viewed wires.

Try disconnecting them one at a time with the engine running and the key off. See if the engine dies.

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Customer reply replied 2 months ago
I already know the answer to that one. That is how I currently have it set up. If I disconnect the 20 amp the engine keeps running if I disconnect the 25 amp it kills the engine through supplication. Basically the sensors quit working and the system just shuts down two or three seconds after I turn the key off. It's how I am working through things at the moment. My thought is there has to be a more direct wire to kill the power with. What wire can I turn the ignition and have been run mode and when I turned it off kills the motor is it a coil wire I'm trying to figure out the key to shut the system off as the key goes off.

What if you move those two wires, to a circuit that is only hot with the key in the run position?

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Customer reply replied 2 months ago
Would I lose my computer's memory? It might affect performance. And I can certainly try and see if it works however. For some reason though, I am leaning towards finding that one wire that just kills the whole system. That's the one I really want to put on the ignition. I won't be able to get back to this until a little later, but if you have any thoughts be sure and share them. Thanks.

I don't know of any wire that kills the ignition. On either the 75 bronco wiring or the 1990 wiring. The way the system is supposed to work is the ignition circuit loses voltage once the key is turned to the off position.

There isn't anything that can apply voltage to cut the engine off.

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Customer reply replied 2 months ago
what do you think about moving those two wires off the Silla Noyd and putting them on a ignition hot. Do I lose my computer settings? Is there a way to prevent from losing my computer settings?

Without knowing where the computer is getting voltage from I would say it most likely won't make a difference. If it's the original obd1 computer from the 1990 bronco then it should store any data on flash memory and losing battery voltage shouldn't affect the way it runs.

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Customer reply replied 2 months ago
I know to clear the computer memory on the EECIV system, I have to disconnect the battery for a period of time. The computer is from a 1990 Mustang if that means anything. It's not data that I am concerned about losing, it is the learning capability of the computer as it learns your driving style. I don't know where that is stored. But, in the meantime I will see if I can get that setup with all EECIV functions running off ignition power. I do have a hesitation in that there is a 20 and a 25 amp fuse in that system. Wouldn't I have to connect to a more robust wire than what I might find under the dash? Seems like a lot runs from those two wires.

The wire from the PCM that is black with an orange stripe is your keep alive memory. If you run that wire only on a constant 12 volt circuit you should be fine.

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Customer reply replied 2 months ago
That sounds like a step in the right direction. Any thoughts on the gauge of wire to use to connect those two computer circuits to the ignition? I was just going to pick up an existing wire behind the dash, but with the power going through those wires I think I should maybe make sure I have a good connection. I can however do a quick setup just to test the idea with the two main wires anyway. If that works, then I'll pick up the KAM wire.

If they power the PCM it shouldn't draw anything more than 15 amps or so. Do you know which two wires they are on your diagram you sent?

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Customer reply replied 2 months ago
Nope. That did not wrk connecting the two wires from the computer.
Customer reply replied 2 months ago
Basically when I shut off the power to the ignition to be 25 amp fuse, I'm guessing I am essentially shutting off the fuel flow which takes about two to05 seconds to kill the engine.
Customer reply replied 2 months ago
Can I run the engine without the light green/red wire going to the alternator? What does that wire do? It originally came from the firewall as a solid green wire, goes in and out of a plug, and turns light green/red then splices to orange wire and then on down to the white lead of the alternator. But the original was green or light green/red on the 75 Bronco wiring.Right now things appear to be functioning properly without that wire connected. My fear is that may damage the battery in some way by overcharging or something? The battery has 12.65 volts, I start the engine and the battery runs at about 14.4 volts, and I can shut the engine off with the key. The problem is that it seems a questionable solution. And what of the white wire then?

It sounds like that might be the source of your back-feed. Where is that wire running to? You should just have the red wire hooked up to the battery and that's it. The white wire on the alternator, that it looks like you also have an orange wire hooked to should run to the dash to run the alternator gauge.

The alternator is internally regulated so it shouldn't overcharge. It is supposed to sit at 14.9 volts (give or take a half volt) all the time when running.

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My little picture never came through when it sent it before.

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It anything else is hooked to the alternator it's unnecessary and is probably causing the problem.

Jared D
Jared D, ASE Certified Technician
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Satisfied Customers: 1,983
Experience: Shop Supervisor at County Fleet
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