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3G Alternator Fox Upgrade

Preface: When the following procedure is complete, the ORANGE/BLACK factory alternator wire WILL NOT BE USED. Whether you cut that connector off or just leave it hanging is up to you (I prefer to just leave it tied up out of the way).

Using the factory ORANGE/BLACK wires on an alternator upgrade can lead to an under hood fire. They're barely able to carry the 75 amps from the factory 2G alternator much less the load from a 3G+ into radiator fans or stereo amps etc.

If you spot an error in this tutorial, please PM me or click on the discussion tab to input comments.

Dan... If you're still out there, hope you don't mind my borrowing this. It's a great writeup and I didn't want to see it lost.

130 amp alternator upgrade

Written by: Dan Acevedo

Equipment upgrades using factory parts have always appealed to me. In most cases, it seems that the upgrade is merely ones correction of what the factory should have done. An example would be the 73mm front brake caliper that everyone has heard of. This upgrade brings the factory brakes up to snuff without breaking the bank. Another popular upgrade of late has been the 130-amp alternator swap. Many enthusiasts, while happy to gain a little extra power with an under drive pulley set, are in the end plagued with battery charging problems. In my case, the drain on the charging system was a combination of under drive pulleys, and a decent sound system, which I have a bad habit of playing while the car is sitting in the driveway.

Most recently, I had to replace a door lock as would be thief’s attempted to break into my car. While these inept hoodlums were unable to gain entry, they did manage to damage my door lock. As it turns out, I discovered that a fellow mustang enthusiast in the area is a locksmith. He rekeyed a lock cylinder and I was set. So what does this have to do with the 130-amp alternator? Well, while replacing the door lock, I had the stereo playing. Also, while I had the door panel off, I checked over the window system greasing the track and such, which required that I run the window up and down a few times. My total time in doing this was 20 minutes. Having successfully completed the door lock repair, I went to start the car. Nothing! The battery had completely drained. I am certain that it was not fully charged due to the inadequate 75-amp factory alternator. While this was not the first time I found myself jumping my car off a friends Mazda truck, It was the last as I vowed to get the highly praised 130 amp alternator.

Ford knew that the stock Mustang charging systems were a problem and decided to upgrade the Mustangs used for police service (Special Service Police). Up until 1991, Ford made the regulators external and a higher amperage to handle the additional loads of police equipment. In 1992, Ford decided to go with the larger 3G style alternator up until the end of the police Mustang in 1993. Here we will show you how we went about upgrading this Mustangs charging system by adding a 1994-1995 Mustang GT 5.0 alternator in place of the stock 75A alternator. There are other applications that use the same alternator but the Mustang is the easiest to remember. One of the most important things to remember about this upgrade is that since the alternator is now able to output 130 amps, it must also have the ability to transfer this power back to the battery safely. The stock Mustang system has two 10 gauge wires that link to one, running to the starter solenoid. This is barely adequate enough for the 75A alternator much less the 130A. Trying to transfer this amount of current through a 10 gauge wire will result in meltdown, burning fuselinks, or potential fires assuming you have enough accessories making the alternator go to full output. Some people have successfully used the factory 10 gauge wire but they have not used the alternator to it's full potential with either a serious sound system, electric fan or even both. I have seen the factory Mustang and other Ford products with the 3G 130A alternator and Ford uses a 6 gauge wire to run from the alternator to the starter solenoid and effectively the battery. They protect this circuit with (2) 12 gauge fuselinks from the factory. Some people have installed a fuseholder with a 150A fuse, but we found it to add more money in the project and has a non-stock appearance. We decided to use 4 gauge wire for an added measure of safety since the wiring will be a little more than 7 feet long. Let us start with the installation after we first disconnect the battery:

Here is the stock 75 amp alternator:

The first step is to disconnect the battery and then proceed to remove the stock alternator. You will notice that the stock alternator is held on by one small bolt on top and one long bolt on the bottom. The 3G alternator does not have a threaded hole for the upper bolt. There are two options we have, either you can run a nut and bolt (3/8" size) or you can heli-coil the hole to accept the stock 3/8" bolt which is what we decided to do here as seen in the picture. Just follow the instructions included in the heli-coil kit if you do decide to go this route. The hole in the alternator is already the correct size, you only need to tap for the heli-coil:

Here is what the alternator looks like with the stock bolt in the heli-coiled hole:

Once the alternator has been removed, we will need to modify the stock bracket since the 3G alternator case is larger. You will need a dremel or other cutting device. If you cannot find one or borrow one, you could do it with a file but you will be working at it for a while. Here are some pics of the clearancing needed for the alternator to fit:

Once the clearancing is complete, you can proceed with the wiring installation. You may have noticed during the trial fitment of the 3G that it was a tight fit in the lower mounting hole. There is a bushing that allows the slack to be taken up with different size alternators. Go ahead and tap the bushing back with a hammer so that the fit will be better. Once you actually mount the alternator and start to tighten the bolt, the bushing will be brought back in by the bolt to the proper position. The question of whether you have underdrive pulleys now comes into play. If you have installed underdrive pulleys on the vehicle, you may not be able to spin the 3G fast enough at idle especially if you are using an electric fan or large stereo system. The owner had a large stereo system and needed all the power he could get at idle. We decided to install the factory alternator pulley from the 75 amp which is smaller in diameter and will allow the alternator to spin faster at idle to give a complete charge. Another nice alternative is an overdrive pulley sold by Auto Specialties that is a mere 1 and 3/4" in diameter. You can elect to use the pulley that comes with the alternator and see what your car requires once under a load.

You will need to remove the factory tape from the harness to expose the union of the two 10 gauge wires which are black with an orange stripe. This D shaped plug with the two large 10 gauge wires also has a very small white with black stripe wire. This wire will be cut off the terminal and used on the 3G in a different location. Once the location of the 10g wire has been found, cut the union and tape or use a butt join to cover up the end of the 10 gauge wire. This wire will still have power since we will need to leave the wire hooked up at the starter solenoid due to the voltage sensing wire that shares the fuse link. This is what your new alternator harness will consist of:

You will leave the D shaped plug alone and have the single white with black stripe wire. The factory harness for the 3G uses a special plug for the small white/black stripe wire. You can get the plug from the local junkyard, use the complete harness available from Ford Racing or use a small female spade connector, it's your choice. We spent part of the afternoon looking for one at the local junkyard, but as you will see it looks much more like a factory installation:

You will need to run your new 4 gauge wire along with the factory harnesses that run in front of the radiator. You can use zip ties or tie straps to hold the new wire to the existing harnesses. The factory wiring goes underneath the battery tray. You may decide to run your 4 gauge under the battery or just run it behind the battery. The owner of the vehicle was looking for a factory installation so the battery tray came out as seen in the picture:

Now comes the time to install the fuse or fuselink you previously decided to use. Here we used two 12 gauge fuselink sections 6 inches long. We used a 4 gauge butt connection with solder to join the wires together and then used heat shrink to protect from short circuits. We got the fuselink wire from Car Quest under part# PW12F. As you can see, it makes for a cleaner installation:

You need to install a ring terminal and install it to the starter solenoid battery side. You can now remount your battery tray if you decided to go the factory way.

Now you can mount your ring terminal to the other end of the 4 gauge and mount it to the alternator stud. Connect the remaining D shaped plug and white/black stripe wire as seen in this picture:

Go ahead and mount your new alternator and make sure your wires are all nice and tied up so that they do not get caught on any moving parts or near any hot header pipes. Once everything is tight, go ahead and install your fan belt and reconnect your battery. Make sure that there are no tools left in the engine compartment and fire it up! You should notice that the amp/battery light will go out and the factory gauge will shoot up a little above the midway point. Your charging system will now be able to handle most anything you can throw at it including the famous Mark VIII fan. The engine compartment looks newer with the installation of the new alternator:

Here is a list of the materials we used:

  • -1995 Mustang GT 5.0 alternator from the local parts store
  • -7 ft of 4 gauge wire from the local stereo shop. This was very fancy wire but was the only wire we could find in such short a time. You can use normal 4 gauge wire.
  • -12 gauge fuselink wire from Car Quest part# PW12F
  • -3/8" ring terminal for 8 gauge wire (for the two 12 gauge fuselink wires to the starter solenoid)
  • -1/4" ring terminal for 4 gauge wire for installation to the alternator stud.
  • -4 gauge butt connector and heat shrink for it. Most large butt connectors (6 gauge and up) do not come with insulation
  • -3/8" coarse thread heli-coil kit for the upper mounting bolt or a 3/8" bolt 1 1/2" long with a nut
  • -convoluted tubing for the 4 gauge wire to protect it from scuffing and for looks :)
  • -factory alternator plug for the stator wire (white/black stripe). Available sources are the local junkyard or Ford Racing
  • -electrical tape
  • -zip ties or tie straps

    Written by: Dan Acevedo
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perfect. love the material list i will be doing this fo' sho'