STICKY: 3G Interchange Facts. Read if you're thinking 3G

[Clarko]

Had to start this thread since there is much misinformation and confusion about the 3G alternator upgrade. This is not an install thread, just a guide on where to get the alt you need, a wiring diagram, and pulley sizing. All photos and some of the text is courtesy of Ryan at FordFuelInjection.com.

Why go 3G?
Because your factory alternator is barely adequate for your truck, stock.
Added off-road lights or a big stereo?
You need a bigger alternator!
Need me to show you?

And that's alternator RPM, not engine rpm. The alt spins much faster than the engine.
Alt RPM = Engine RPM x Crank Pulley Diameter ÷ Alt Pulley Diameter.
Our factory alternators do not even come up to the bottom line unless you have the factory upgraded alt which will only come up to the botom line.

There are 3 different mounting styles for the 3G alternator that can be used as an upgrade on other vehicles:


To fit our v-belt trucks: or anything with v-belts, you'll need a [b]Pivot Mount w/ 8.25â€Â

[460 crew]

Most interesting

[Clarko]

Yeah I spent many an hour creating that for my Bronco forum (www.fullsizebronco.com) so I decided that ya'll could benefit from it too.

[FORDification]

Very nice, Brian....thanks for posting this!  

[bluef250]

I would like to say that Brian did a great job with his initial post.  I have looked at the post several times at the Bronco Site in trying to find the best way for installing a 3G.  

The best 3G 130 amp install diagram I have found is for a 1965 Mustang (from FordMuscle.com forums - Vinyl66 06/23/05).  http://www.fordmuscle.com/TechDepartment/engine.php

http://www.fordification.com/galleries/ ... nstall.jpg

One difference is that they show "A" wired direct to the starter solenoid not to alternator post.  That wiring gives a better balance between the battery and alternator as the alternator senses voltage.

Another point is the 560 ohm resistor inline from the ignition switch which assures that the alternator will start charging.  

Also, make sure the power cable is large enough (6 ga min) and that you have a fuse or a fuse link inline between alternator and solenoid.  

I have found one other person who has installed a 3G on an FE engine.  He said that he had to shim the pulley and shave (mill) a little off back side for clearance.  I think a bottom mount alternator would solve the clearance problems.  

I think with a little creative wiring that the stock alternator gauge would work and that you could also add an idiot light.  The light does have some advantages.  I plan to add a volt meter also.  By attaching the stock charge wire, you keep the amp gauge working plus provides additional capacity for the charging (probably overkill and other changes will be needed.)  The idiot light is an bulb wired in parallel and placed in the instrument panel.  Since the stock amp meter is anemic, I will install larger gauge wire - still protected with 3 amp - fuses to see if I can get more movement.

[68F250]

Thanks for posting that Clarko!

Another point is the 560 ohm resistor inline from the ignition switch which assures that the alternator will start charging.

I was gonna mention that too bluef250!  Without the resistor in there, if the bulb burns out the alt. doesn't start charging.

[Clarko]

The A wire doesn't matter which side it's wired to with a big charge cable such as I recommend the 2 gauge. You will have to shim out the pulley with a small washer or file a little bit off of the alt case, as I did.

I put one on a 390 in my good bud's 56 F-100. It was a painless install.

[bluef250]

Brian,

I think you are correct that the 2 awg would eliminate any losses and that it would not necessarily matter which end the "A" was connected.  One point made by some posts that I have read is that the whole charging system is balanced.  By achieving some balance and buffering between the alternator, battery, and regulator the wiring system acts as a shock absorber and the system as a whole works smoother.

Have you had any problems with the single drive V belt?  When charging over 100 amps, would a single belt be overloaded?

[Clarko]

I've had no problems whatsoever with the single belt although some people claim to need dual belts. That truck is also running the now-famous Taurus fan from the same car.

[kid]

As an electrician the wire sizes quoted are a Tad off.

65 Amp alternator needs 6ga
100 Amp - 3ga
125 or 130 Amp - 1 ga.

The wire if too small will act like a resistor and get hot if the amount of current flowing is more than the wire is made for.

All current going out must come back.  So the engine needs a cable at least as big as the battery cables.  Otherwise the alternator will not be able to produce full current.  Both battery cables must be the same size.  The body cable can be smaller like 8 quage or a couple of 10s like Ford originally used. Unless you have a hot stereo in the cab along with the amplifier.  With lots of roof mounted lights increase the ground wire size on the cab.  

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P.S. A major cause of electrical glitches we have on these old F series are rusted ground wire mounting pads

[Clarko]

Well from the factory Ford installs these with like 4 or 6 ga wires from the factory (not kidding) and I've never had a problem with the 2 ga getting hot.

[kid]

They base the wire size on potential draw of current.  Look at the little wire that comes off the Alternator terminal.  They are not trying to power the truck with the alternator they are only trying to charge the battery with that little wire.

My truck still has 4 guage wire but I have a plain jane electrical requirement.  At least for 5 more months.

[Clarko]

No, I wasn't doubting you at all. I was just mentioning the fact.

[kid]

I know I was just spreading way too much technical information as I am often doing.

[marz68]

3G's rule, I put one in my 89 mustang and on my 68 f100 when it had the original 390 and now it's on my f100 with the fuel injected motor, I also put one on my friends 67 lincoln that has a 460. I used 90's  taurus alternators for all of them cuase of the way the mounting points are.