3g upgrade question.
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From: Wenatchee, WA
3g upgrade question.
Hey there, let me start off by saying i am an electrical idiot. So i get confused with this stuff really easily. I am upgrading my 60amp Alt on my 79 f150 to a 3g setup. The old alt had 1 wire going from 1 terminal, to another, and then to the relay on the passenger side of the box. That was it. Needless to say that wasnt cutting it and i took it out and etc etc etc. Anyways, my dad is a wireman/electrician going on 20+ years so anything you tell me i can pass on and he'll no what to do. my big question is on the wire that i have to hook up to my ignition, I have an msd blaster 2, which has the 2 wiring terminals. Which one would i put it on? 
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From: Virginia
Neither one. The trigger wire from the alternator can backfeed voltage, so if you hook it to the coil you may find the engine won't turn off.
What condition is the original 79 harness in? It originally came with a external regulator type system. If you still have the external regulator and/or it's wiring plug, look for a green/red wire. If you find it, get your Dad to put a voltmeter on it while you turn the key to run. It should have 12v on it when you turn the key. If it does, this is the wire you need to use on your new 3g alternator.
What condition is the original 79 harness in? It originally came with a external regulator type system. If you still have the external regulator and/or it's wiring plug, look for a green/red wire. If you find it, get your Dad to put a voltmeter on it while you turn the key to run. It should have 12v on it when you turn the key. If it does, this is the wire you need to use on your new 3g alternator.
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From: Wenatchee, WA
Neither one. The trigger wire from the alternator can backfeed voltage, so if you hook it to the coil you may find the engine won't turn off.
What condition is the original 79 harness in? It originally came with a external regulator type system. If you still have the external regulator and/or it's wiring plug, look for a green/red wire. If you find it, get your Dad to put a voltmeter on it while you turn the key to run. It should have 12v on it when you turn the key. If it does, this is the wire you need to use on your new 3g alternator.
What condition is the original 79 harness in? It originally came with a external regulator type system. If you still have the external regulator and/or it's wiring plug, look for a green/red wire. If you find it, get your Dad to put a voltmeter on it while you turn the key to run. It should have 12v on it when you turn the key. If it does, this is the wire you need to use on your new 3g alternator.
Is this what your talking about? Its the source that the old alternator was wired to. We took the voltometer to it and only got 3 volts. But then we put it on my battery and only got 4v cause its dead. :P
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From: Virginia
No, your arrow is pointing to the starter relay(solenoid). They also use the solenoid as a connection point for battery + feeds, so that is why the alternator output wire and some others are there.
The original regulator looked like this;
If it's not there, you still should have a wide flat plug with wires that plugged into this unit. That's where the lightgreen/red will be located.
The original regulator looked like this;
If it's not there, you still should have a wide flat plug with wires that plugged into this unit. That's where the lightgreen/red will be located.
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From: Wenatchee, WA
would this be it? This is the only thing i can find that looks remotely like the regulator in the picture. This on is under my dash. It doesnt have any red/green wires though.
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From: Virginia
No, you can tell from the connectors that's not even original. The original regulator was usually mounted on the passenger side inner fender under the hood, or on the front support beside the radiator. So keep looking under the hood for the green/red wire.
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From: Wenatchee, WA
I'm not finding anything like that anywhere.,,
Is there a possibility that there is no voltage regulator on there now? and i found a red wire that butt crimps to a green wire but its not being used so i doubt that is it.
Is there a possibility that there is no voltage regulator on there now? and i found a red wire that butt crimps to a green wire but its not being used so i doubt that is it.
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From: Virginia
Your truck's harness under the hood must be a real mess. I think you have two options;
1. If you can look at a similar year truck or Bronco that is mostly original, you can probably figure what was originally supposed to go where and make a rough drawing with wire colors. Then you may be able to find it in your harness, or
2. Continue on with the homemade wiring, and run a wire from the fuse box from something in the fuse box that turns on and off with the key, and run this wire out to trigger the alternator. Depending on where you pick the key-on power up, the engine still might not turn off, or when you turn the key to off, it will take several revolutions of the engine before it stops. If you have this problem, you can install a diode in the line to prevent this from happening.
I don't like to even think what type of ignition system you have, and how it's wired up(I see the coil is mounted on the inner fender) but most ignition systems are fed by a special resistance wire in the harness, and that's why you cannot use it for the alternator trigger, even if you put the diode in place.
1. If you can look at a similar year truck or Bronco that is mostly original, you can probably figure what was originally supposed to go where and make a rough drawing with wire colors. Then you may be able to find it in your harness, or
2. Continue on with the homemade wiring, and run a wire from the fuse box from something in the fuse box that turns on and off with the key, and run this wire out to trigger the alternator. Depending on where you pick the key-on power up, the engine still might not turn off, or when you turn the key to off, it will take several revolutions of the engine before it stops. If you have this problem, you can install a diode in the line to prevent this from happening.
I don't like to even think what type of ignition system you have, and how it's wired up(I see the coil is mounted on the inner fender) but most ignition systems are fed by a special resistance wire in the harness, and that's why you cannot use it for the alternator trigger, even if you put the diode in place.
Thread Starter
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Senior User
Joined: Jan 2010
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From: Wenatchee, WA
Your truck's harness under the hood must be a real mess. I think you have two options;
1. If you can look at a similar year truck or Bronco that is mostly original, you can probably figure what was originally supposed to go where and make a rough drawing with wire colors. Then you may be able to find it in your harness, or
2. Continue on with the homemade wiring, and run a wire from the fuse box from something in the fuse box that turns on and off with the key, and run this wire out to trigger the alternator. Depending on where you pick the key-on power up, the engine still might not turn off, or when you turn the key to off, it will take several revolutions of the engine before it stops. If you have this problem, you can install a diode in the line to prevent this from happening.
I don't like to even think what type of ignition system you have, and how it's wired up(I see the coil is mounted on the inner fender) but most ignition systems are fed by a special resistance wire in the harness, and that's why you cannot use it for the alternator trigger, even if you put the diode in place.
1. If you can look at a similar year truck or Bronco that is mostly original, you can probably figure what was originally supposed to go where and make a rough drawing with wire colors. Then you may be able to find it in your harness, or
2. Continue on with the homemade wiring, and run a wire from the fuse box from something in the fuse box that turns on and off with the key, and run this wire out to trigger the alternator. Depending on where you pick the key-on power up, the engine still might not turn off, or when you turn the key to off, it will take several revolutions of the engine before it stops. If you have this problem, you can install a diode in the line to prevent this from happening.
I don't like to even think what type of ignition system you have, and how it's wired up(I see the coil is mounted on the inner fender) but most ignition systems are fed by a special resistance wire in the harness, and that's why you cannot use it for the alternator trigger, even if you put the diode in place.
and that single wire went back to the relay
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From: Wenatchee, WA
"it has a one wire gm alternator its internally regulated" Actual quote from the PO
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