Mustang MonthlyHow To Interior Electrical
How to Identify and Select Ford Alternators
Make the most of your Mustang’s charging system by making the right charging system choice
Mustangs have had alternator charging systems since August 1964, when all Fords and Mercurys became so equipped. Alternators are clearly better than generators in that they maintain a steady charge at all engine speeds, including idle.
In the beginning, Autolite 1G alternators, which were rated at 38-55 amps, didn’t have much to keep up with. There was the radio, heater, lighting, occasionally horns, and the ignition system.
Today, alternators have a much larger job to do thanks to all the accessories we like to install in automobiles that offer the comforts of home. When you start adding subwoofer sound systems, power windows and locks, high-intensity headlights, electric cooling fans, and the rest of it, it can make an older Autolite 1G alternator sweat with anxiety trying to keep up with the load.
Whether you’re restoring a classic Mustang or building a hot restomod, it’s important to know a bit about Ford-based alternators and how they have evolved over the last 50 years, then make the right selection for your application. Cool thing is, you can uprate an older 1G 38-amp to 100-amp with the right parts, or fit your classic with an uprated 1G for a stealthy improvement.Alternator selection boils down to electrical demand. Output must be greater than demand or you wind up with dim headlights and a dead battery.
Showroom stockers can get by with original equipment—the externally-regulated Autolite 1G common from 1965 to 1986 are all interchangeable. In 1982, Ford stepped up the charging system demand with the internally regulated 2G alternator, which looks basically like the 1G, only with a 2G-specific wiring harness. The 2G was common to all Mustangs from 1986 to 1993. It was replaced by the 3G in 1994, then the 4G and 6G later.
Not only were there differences in amperage rating, but also pulley sizing, width, and type, in either one-groove or two. Most small- and big-block Fords had a 2.62-inch-diameter, single-groove pulley. The 289 High-Performance V-8 alternators had a larger 3.87-inch- diameter, single-groove pulley to reduce rotor speed at high rpm. Dual-groove pulleys are 3.15 inches in diameter—slightly larger than the single groove. Pulley size, number of grooves, and amp rating depended upon application.
Alternator fan type is also very important to both identification and function. We see so many rebuilt Autolite 1G alternators out there with incorrect fans for the production time frame, and we’d like to set that straight.
According to Jack Brooks at www.deadnutson.com, fan type depends on when the alternator was manufactured, and this is easy to see at a glance. Those first 1G alternators had the flat 13-blade fan used before March 1965. Beginning in March 1965, a more sculptured (stronger) 13-blade fan was used on the 1G. Beginning November 17, 1969, the 1G got a 10-blade fan (fewer, wider blades), which was used through the end of 1G production in 1986. This 10-blade fan was also used on the internally regulated Motorcraft 2G alternator from 1982-1992.
1G AlternatorAlternator use and application gets complicated with the 1G. Because these 1G cores have been so scattered through rebuilds and salvage yards over the years, expect to see a wide variety of mismatched parts. The rounded case 1G Ford/Autolite alternator was used from mid-1964 through the ’71 model year. Beginning with the changeover to Motorcraft in 1971-1972, Ford redesigned the 1G case with a square corner housing, which was used through the end of 1G production in 1986.
You will see mix-matched round and square housings, 10-blade fans with round cases, 13-blade fans with square cases, and so on. If you’re not concerned with originality, none of it matters—it is all interchangeable and will function just fine. However, if you’re looking for correct period parts, that’s a challenge. It’s a crap shoot when you buy a 1G from a discount auto parts store. You may get exactly what you want or wind up with a mix-matched case combination.
If you have an Autolite or Motorcraft 1G alternator original to your Mustang, there are excellent resources where it can be rebuilt and massaged to perfection. You may also buy a rebuilt 1G at a discount auto parts store and swap its components into your original case, especially if you’re concerned about losing your case to a rebuilder.
The 1G is pretty consistent throughout its production history, along with the Mustangs it bolts into. Where the 1G gets tricky is the ’84-’86 Mustang SVO, which is 1G-equipped but wired differently between the alternator and voltage regulator. You are better off having your 1G rebuilt by a trusted source.
Although purists and restorers have spent a lot of time trying to sort out 1G alternator case differences, there are no pat answers. Some have Autolite on them, while some don’t. Some have the teardrop at the rear of the case, while others don’t. There are aftermarket 1G cases as well adding to the confusion. Ideally, you will find a complete 1G core or castings appropriate for your restoration.
Autolite versus no-name boils down to whether it was factory installed or a service replacement, though that isn’t even completely true. Assembly plants installed whatever was in the parts pipeline and no one cared.
And again there’s the confusion of aftermarket versus genuine Ford. It takes savvy eyes to spot what’s correct and what isn’t.
2G AlternatorThe Motorcraft 2G internally- regulated alternator (known as “firestarter” and “flame-thrower” among enthusiasts) was introduced in 1982 on full-sized Fords and Mercurys, later working into the Mustang beginning in 1986, with 5.0 liters and fuel injection.
Although we’re showing you the 2G, it is strongly suggested you step up to the 3G unless you’re performing a concours ’86-’93 Mustang restoration. It is also suggested you periodically inspect the 2G’s multiplex plug and wiring for heat and decay.
The 2G’s biggest problem is under-capacity and wire size that just isn’t up to the job. When you add corrosion issues to this connector, resistance increases and heat becomes a major (and dangerous) issue. Do not use your 2G’s wiring and plug for the 3G conversion—it is not of sufficient capacity to handle the electrical load and will start a fire. Rick Harmon of PA Performance suggests upgrading to the 3G if you’re in a position to do so and don’t mind replacing the factory 2G unit.
3G AlternatorAsk anyone about 3G and they might get it confused with the older cell phone network. However, Ford’s 3G high-amp alternator is the sweetest solution for anyone looking to boost charging system output in an afternoon.
The Motorcraft 3G alternator is available from a number of sources. PA Performance, Powermaster Performance, Performance Distributors, and Summit Racing Equipment are all excellent sources for 3G alternators and conversion kits.
There are plenty of reasons why you should replace your 1G or 2G with the 3G. The 3G will handle just about any size electrical load you can imagine, whether you have a classic or late-model Mustang. The beauty of the 3G is idle speed output and fitment. It delivers plenty of amperage at idle, and can deliver as much as 230 amps depending on where you source your 3G.
4G AlternatorThe Motorcraft 4G pancake-style high-output alternator, which looks similar to the 3G, is available from PA Performance and Performance Distributors for Modular engines, small-blocks, and big-blocks. It is more compact than the 3G and produces more amperage.
6G AlternatorThe Motorcraft 6G alternator arrived on the Mustang for the ’99 model year (4.6-liter two-valve) and has been a mainstay ever since. The 6G is a super-high-output alternator designed more specifically for late-model Mustang applications with the 4.6L, 5.4L, and the Coyote V-8. There is virtually no reason to apply it to your classic Mustang application.
Autolite or Motorcraft?Ford’s Motorcraft name originated in the ’50s; however, it was not very successful. In 1961, Ford acquired the Autolite name, along with its assets, including a spark plug manufacturing facility and a battery factory. Ford very quickly began using Autolite products as original equipment in new vehicles. In the years to follow, Ford would be involved in a lengthy federal anti-trust lawsuit that ended in 1971 when it was forced to sell its Autolite Division to Bendix.
When Ford sold Autolite, it came up with a marketing solution known as Motorcraft. It brought back the old name and managed to make a success of it. This is why the Motorcraft name appeared for the second time beginning in 1972. This is also when the 1G alternator became a square case with the Motorcraft name. The Motorcraft name did wind up on some round-case alternators toward the end of round-case production in 1971-1972.
Motorcraft Alternator Quick Reference1G: 1964-1986
The original Ford alternator rated at 38 to 55 amps. It is externally regulated. It can be upgraded to 65, 95, 130, or 200 amps, though you are better off going to the 3G if you want over 95 amps.
The 2G is the second generation Ford alternator, internally-regulated with multiplex plug in 65- and 75-amp ratings. It can be upgraded to 130 and 200 amps, though not recommended. The down side is the underrated plug and wiring, and corrosions issues that cause high resistance, heat, and fire.
The best bang for the buck there is for classic, Fox, and ’94-’98 Mustangs alike. The 3G is an outstanding alternator for the money and is easy to install in any application. Never use the 2G plug in a 3G swap. It will overheat and catch fire. The 3G is available in 130 and 200 amp ratings.
The 4G is a pancake version that looks like the 3G, which makes it ideal for tight installations. The 4G is available in 150 and 200 amps, and was OE on the ’96-’02 four-valve Modular and Bullitt models.
The 6G arrived on the ’99 Mustang and could also be found on the ’02-’04 four-valve Modular. It was also used on the all-new S197 Mustang for 2005. It is designed primarily for late-model Mustangs. It is available in 130-, 170-. and 200-amp ratings.
Alternator Output RatingsInformation courtesy PA Performance
|Engine RPM||1G 60-AMP||2G 75-AMP||3G 95-AMP||3G 130-AMP||3G 200-AMP|