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Old 11-02-2008
RLG34750's Avatar
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Alternator Upgrade .....DIY

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

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. 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

list of the materials
  • -1995 Mustang GT 5.0 alternator from the local parts store
  • -7 ft of 4 gauge wire
  • -12 gauge fuselink wire
  • -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

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