3G Alternator Install: A How To

satanas · Oct 22, 2011

Sorry I have a question also...I have my battery. And solenoid in trunk...at the Moment I have an 8 gauge running to where the original solenoid was to run all the accesories a distribution block I. Guess not sure what's it called.....now do I need to run a 4 gauge to the distribution block then to the battery or can I just run it staright back to the solenoid.its less wire if I run it back to the rear..sorry for hijacking thread but it does have to do with 3g installation..lol..thanks..

86gtriceeater · Oct 22, 2011

I would just do it right the first time. 4gauge to the distribution block then to the solenoid with an inline Mega fuse close to the battery

satanas · Oct 22, 2011

So the 4 gauge would replace the 8 gauge that I have at the moment that goes to thesolenoid to the dis.block??

86gtriceeater · Oct 22, 2011

I believe with the 87-93 you'd replace the 8guage w 4gauge and omit that old wiring. Also make sure you also have a 4guage ground at the battery pigtail near your windshield washer fluid reservoir.

satanas · Oct 22, 2011

Thanks for the fast response......the 8 gauge wire wasn't stock it was in sme instruction I read many years ago I've been running that on my mustang...I have my battery in the trunk.solenoid inthe trunk and I have a mini starter.so my wiring changed...I have a battery ground ...a original ground from head to back of firewall and 4 gauge from block to cntrol arm bolt... I think. Running the 4 gauge is understandable since I would be running an electric fan and msd box which I haven't tried out yet with my stock alternator... thanks again.....

Jason 302 · Feb 15, 2012

I just tried to do this conversion tonight. Everything was going well until I went to hook the 4 gauge wire going from the post of the alternator to the starter solenoid...I'm getting sparks/arcing really bad. I've went over jrichker's diagrams and I have everything wired according to those....anybody have any ideas? I'm no good at electrical stuff.

Jason 302 · Feb 15, 2012

I just realized it's arcing because the outpost of the alternator is acting like a ground, and hooking it up to the positive side of the battery is obviously what's causing the sparking. So how exactly does that work then? How is the charging post of the alternator suppose to charge when it acts like a ground?

LarsD · Feb 15, 2012

Jason 302 said:
I just realized it's arcing because the outpost of the alternator is acting like a ground, and hooking it up to the positive side of the battery is obviously what's causing the sparking. So how exactly does that work then? How is the charging post of the alternator suppose to charge when it acts like a ground?

If that is the case, something is wrong with your alternator or wiring. Are you hooking it up to the forward post or the rearward post?

Jason 302 · Feb 15, 2012

Forward and rearward? Are there two posts on the alternator? The only one that I seen was surrounded by red plastic, so I assumed it was the charging post. As far as battery wise, it's going to the positive (+) side.

LarsD · Feb 15, 2012

Jason 302 said:
Forward and rearward? Are there two posts on the alternator? The only one that I seen was surrounded by red plastic, so I assumed it was the charging post. As far as battery wise, it's going to the positive (+) side.

My bad, I meant on the starter sileonoid.

jrichker · Feb 15, 2012

If you get a spark when connecting the 4 gauge wire to the Battery side of the starter solenoid, you have an alternator with a bad diode or the 4 gauge power feed wire is shorted to ground somewhere. Pull the alternator off and take it to someplace like AutoZone or Advanced Auto Parts and have it bench tested.

Make sure that the 4 gauge wire terminal isn't shorted up against the alternator frame where the terminal bolts on the the alternator.

Jason 302 · Feb 15, 2012

Okay, so I'm an idiot. Turns out the connector on the end of my 4g wire was barely touching the base of the alternator, causing it to ground. Once I got that sorted, I got it finished! Wow....I can't believe I've waited almost 10 years to do this mod. It no longer discharges at idle (even with underdrives) and the fuel pump no longer bogs down while the car is idling....lol. I honestly don't see how the stock 75amp has been supporting me all these years...especially with an electric fan

Jason 302 · Feb 15, 2012

Yup...you got it J. Too bad you weren't an 1/2 hour earlier...you would of saved me a little head scratching lol. Thanks!

jrichker said:
Make sure that the 4 gauge wire terminal isn't shorted up against the alternator frame where the terminal bolts on the the alternator.

jrichker · Feb 16, 2012

Success is beautiful music to everyone's ears. Glad you got it fixed.

Blown88GT · Feb 16, 2012

Just make sure the nut on the power connector is very tight. If it comes loose, it will destroy the diode pack.

Jason 302 · Feb 16, 2012

I put a little blue loctite on there to be safe. I also cover the 4 gauge cable with some ribbed wiring cover....looks factory. This is a pretty simple mod when you don't ground out your charging cable lol.

Mark Cappello · Jun 15, 2013

Hello, I have read thru this thread a few times. I just want to clarify something, and ask a question as to how it works.

It seems there was different posts on how to successfully wire up a 3g alternator in a fox mustang. It seems as if it depends on whether you are going to reuse the existing 2g harness in the mustang , or if you got a 3g pigtail harness.

If you intend to reuse the existing harness, then the connection that has the two black orange wires gets taped up on one end, and remain connected on the starter relay at the other end, while the black white wire can either get cut and connect to stator port on alt or can have a Y splice and still connect to the stator port. ANd a 4 gauge wire runs from alt power post to mega fuse to starter relay bat terminal or directly to bat post. The other connector from the 2 g alternator gets hooked up to the 3g alt the same way with no modifications.

if you got a new 3g pigtail with your new 3g alternator, the new pigtail has a black white wire that just loops over to the stator terminal on alt, a yellow wire that loops over to the alternators batt post on the back of alternator, and the green wire gets connected to the green red original harness wire in the other connector. And the other original 2g harness connector gets all three wires taped off.. the two black orange wires and the white black wire. And you still leave the other end of that connector connected to the starter relay, even though your not using the black orange wires or the white black wire, because it has a fusible link in that harness that the green red wire is also somehow connected to.

what i don't understand is what the wiring does, and what the sensing wire does, and why certain wires need to have fusible links,

MikeH686 · Jun 16, 2013

The reason for the sense wire is when there is current going to it it let's the alternator know when to turn on its more or less a turn on wire like for an amp in a car.

Mark Cappello · Jun 16, 2013

the sense wire is connected to the bat terminal post on the back of the alternator which also has a 4gauge wire connected to the battery positve post of the starter relay on the other end of that wire so it will always have current going to it. It will either see 12 volts from the battery from that post, or it will see volts from the alternator coming out of that same batt post. so how can it tell the alternator when to turn on when it senses current since there is always juice on that post regardless if the engine is running or not and regardless of whether the key is turned to on or not?

and in the oe stock 2g wiring diagram there is a 18 gauge fusible link in the yellow wire on the original 2g wiring harness, but on the 3g alt with a 3g pigtail there is no fusible link, the yellow wire just loops over from the alternators battery post over to the other D terminal connector.

the green/red wire is the exciter wire. what exactly does that do? i thought that wire gave the regulator juice to turn that part on. what part exactly in the alternator is the sensing wire turning on?

jrichker · Jun 17, 2013

Alternator wiring circuit
Notice the green wire connects to a switched power source. The circuit contains a 500 ohm resistor in series between the switched power and the alternator. Connecting it to switched power keeps the regulator from drawing current when the engine is not running. The resistor limits the current flowing through the wire so that a fuse isn't needed if the wire shorts to ground.

Also notice the sense wire connects to the starter solenoid and it is fused. It connects to the starter solenoid so that it can "sense" the voltage drop across the output wiring from the alternator.

3G Alternator Install: A How To

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