Mustang Electrical Info
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3G 130 amp alternator upgrade:
This is a step by step article on how to install a 3G alternator in place of the stock 75A alternator. Itís no secret that the stock 87-93 Mustang charging systems were a weak. Ford upgraded the SSP (Special Service Police) Mustangs with better charging systems. Until 1991 SSP Mustangs had higher amperage alternators an in 1992 and 1993 Ford went with the larger 3G style alternator. So the first obvious benefit to upgrading to a 3G alternator is the 130 amp output which is great, especially if you have a big stereo system and other high load electrical devices. Another benefit is looks. The 3G looks so much nicer than the factory fox body alternator. The last benefit is safety. If you have ever replaced an alternator on a fox body Mustang (or other Ford vehicles using this style alternator) you will notice that every replacement alternator comes with a new connector to replace the old connector. Most likely some sort of warning also came with the alternator and connector telling the dangers of not replacing the factory connector. These dangers include premature alternator failure, shorting out and fires. The reason for these dangers is in the factory connector there are two terminals in the connector which split the current coming from the alternator. These terminals commonly become corroded or worn which causes resistance. This resistance causes heat which can melt the wiring and cause a fire. Itís not something that can happen, itís something that does happen. The 3G alternator eliminates that poorly designed factory connector.
There are many Ford vehicles that use a 3G alternator. You can buy a new 3G alternator from an auto parts store or you can buy a used one from a salvage yard. If you go hunting for one at a salvage yard, make sure you clip the small white stator plug and take that also. You will need it.
- 94-95 Mustang V8
- Mid 90s Taurus and escort. Says 130A on the
back etched into it.
With this upgrade the new alternator will be capable of 130 amps versus the stock 75 amp unit which is going to be too much for the factory wiring. The stock fox body Mustang uses two 10 gauge wires out of the alternator that merge into one wire which delivers electricity to the starter solenoid to charge the battery. While this set up works on the stock 75 amp system, it is really pushing the issue of safety when you run a 130 amp alternator. Issues that could result from this are blown fusible links, fires, etc. If you donít use the alternator to its fullest potential this probably wonít be an issue but if that was the case, why would you want to upgrade anyway? Do it right, do it safe and use a 4 or 6 gauge wire.
1. Disconnect the battery.
2. Remove the serpentine belt.
3. Remove the stock alternator. This is fairly simple. First remove the two electrical plugs from the alternator. Now you can remove the mounting bolts. There is a short bolt on top on the back side of the alternator holding the alternator to the accessory bracket. There is also a long bolt on the bottom of the alternator that holds the alternator to the bracket. You will need a 9/16Ē wrench for the top bolt and a 5/8 wrench or socket for the lower bolt. After removing these bolts you can remove the alternator. You may have to wiggle it a bit to get it to come out. The upper radiator hose is in the way but you can easily pull it back out of the way.
4. Modify the stock accessory bracket to accept the larger 3G alternator. An angle grinder, die grinder or dremel tool will work. Fit the 3G alternator in the bracket to see where you need to clearance the bracket. The triangular section of the bracket is where the problem is. This modification will not affect the strength of the bracket. You might run into an issue with the bushing in the lower mounting hole as well. If the 3G doesnít fit in the lower mounting hole, you can tap the steel bushing in a bit so the alternator slides in. This is a slack adjuster of sorts and is there so different alternators can be used in the same bracket. Donít worry if you tap it in too far because once you tighten the lower bolt it will snug the bushing back up against the alternator. Once you finish clearancing, you can install the alternator and tighten the bolts. Some 3G alternators do not have a threaded top hole. There are two solutions for this. One solution is to use a 1 1/2Ē long 3/8 bolt nut with a washer on each end. The other solution (which looks nicer and more professional) is to tap the existing hole and use a helicoil so you can thread the bolt in like your original alternator. The unthreaded hole in the alternator is already the correct size for the helicoil so you wonít need to do any drilling. Now its time to move on and start modifying the charging system wiring.
5. Wiring modifications. Remove any tape and conduit from the wiring harness on the D-shaped plug to expose the two 10 gauge (black w/orange stripe) wires. These two wires come out of the rectangle connector and then join to one wire. Cut the wires where they join into one which will leave the two wires on the rectangle connector. This will leave you with a single 10 gauge wire. This wire will still have power because it shares a fusible link with another wire at the starter solenoid. You can go thru the work of chasing the wire back to the solenoid and cutting it there or you can simply tape the end off where you made the cut. You can also use a butt connector to cover the end of the wire. In this harness you will also find a smaller white wire with a black stripe. This is the stator wire. Cut the stator wire off of the factory rectangle connector and discard the connector. This stator wire is on a separate connector on the 3G alternator which you can find at a salvage yard and possibly at an auto parts store. If you canít find a factory plug anywhere, you can use a female spade connector. The D-shaped plug from your factory alternator will plug right into your 3G alternator so you can go ahead and plug that in now.
Now its time to run your new power (4 - 6 gauge) wire. You can run it along the factory conduit in front of the radiator or you can make it nicer install and actually run the wire thru the conduit so everything looks like it came from the factory that way. If you choose to run the wire inside of the factory conduit you will need to remove your battery and battery tray as the factory conduit runs underneath it. After you are done running your new wire you can secure the factory harness in place and reinstall the battery tray and battery if you removed them.
When you connect the wire to the starter solenoid it would be wise to use a fusible link or an inline fuse (150 amp) in case the wire or alternator would short out for any reason. Always solder wire connections and use shrink tube to cover the connection. Now you can install a 3/8 ring terminal on the end of the wire and connect it to the battery side of your starter solenoid. Then install a 1/4 ring terminal on the other end of the new power wire and connect it to the alternator post. Go back and double check your installation. Make sure the wires donít get in the way of any hot or moving parts. Tape up the new wires at the alternator nice and tight just like the factory harness was.
6. Install your serpentine belt and then reconnect your battery.
7. Youíre done! Now you can start the car and check your voltage.
Underdrive pulley note: If you have underdrive pulleys on the car you may not be able to spin the 3G fast enough at idle especially if have a large stereo system. This same problem exists with the factory 75 amp alternator. You might want to consider using the factory pulley from your original 75 amp alternator if your underdrive pulley gives you any charging issues at idle.
Problems after 3G upgrade? Are you having voltage spikes or flickering headlights after a 3G upgrade using a remanufactured alternator? A potential problem could be an internal flaw in the alternator which is a pretty easy fix. The windings inside the alternator pass by a sharp ridge inside the alternator. Some companies use cheap materials to insulate these wires and some use nothing at all to insulate them. In time, vibration can cause contact between these wires and the ridge. The contact causes a temporary short which can cause headlights to flicker, stereo to cut out, etc. What is the solution? If you buy a remanufactured alternator flip it over and push the wires forward away from the alternator case using the vent holes in the rear of the alternator. Problem solved!
Here is a list of items you will need for this swap:
feet of 4 or 6 gauge wire. You will only need about 7 feet but its nice to have
extra just in case.
ring terminal connector
Poor grounds can cause a variety of problems such as hesitations caused by intermittent EFI problems, erratic gauge fluctuations, charging problems, alternator overload, headlight and interior light dimming as well as other problems. A bad ground can affect starter performance as well. There are a few things you can do to create better grounds in your electrical system.
Make sure you have a ground loop. Run a cable from your negative post on the battery to the engine block then from the engine block to the frame and then from the frame to the negative battery post. Doing this will increase the life of your electrical equipment, increase accuracy of sensors and gauges and can cure radio noise issues. Also make sure that all ground connections are free of paint, rust, dirt or anything else that will get in the way of good clean metal to metal contact. Missing any one of these grounds can cause the problems outlined above. On a Mustang, the ground strap that connects from the driver side cylinder head to firewall is often the culprit for dimming lights or gauge fluctuation due to corrosion, broken cable or the cable physically missing. The ground connecting the frame to the battery is equally important on a Mustang because it connects to the same spot as the EEC ground on the inner fender. When a 3G alternator upgrade is done an additional 4+ gauge wire should be run from this location to the engine block. The EEC ground that shares the connection with this ground can cause a multitude of problems if it becomes disconnected, broken or the connection is corroded so it is a good idea to inspect this wire while you are working on the ground system. A little way down the wire there is a round connector that resembles an older style glass fuse connector which sometimes becomes disconnected. Some problems that can be caused by bad connection on this wire include stalling and fuel pump only running while the key is in the "crank" position and not running when the key is in the "run" position.
Upgrading battery cables to fine stranded cables are more dense than standard cables which will increase conductivity, reduce electrical resistance and be more heat resistant. Fine strand cables are also more flexible and easier to work with when you are running cable thru the car a rear mounted battery. Use at least 1/0 gauge cable. Bigger is better. Use star washers at every connection if possible. These washers dig in and clamp better.
*3.8 Taurus fan - moving 3750 cfm at 34 amps
*Lincoln Mark VIII fan - 4300 cfm at 42 amps (100 amp start up) and 2200 rpm
*Flex-a-lite Black Magic #175 Ė 2800 cfm at 13 amps and 2200 rpm
*Flex-a-lite Black Magic Xtreme #185 Ė 3300 cfm at 18 amps and 2450 rpm
Ignition switch Ė red is key on 12V power and white is cranking 12V power.
87-93 stereo wiring:
pin# wire color application
1 yellow 12 volt constant - memory, clock, battery
2 not used
3 red 12 volt ignition (switched)
4 orange dash lights (illumination)
5 not used
6 black radio chassis ground
7 blue power antenna
8 not used
1 white left front positive
2 white/black left front negative
3 green left rear positive
4 green/black left rear negative
5 gray right front positive
6 gray/black right front negative
7 violet right rear positive
8 violet/black right rear negative
Mustang instrument cluster wiring - click here for PDF