Category: alternator

How to Identify and Select Ford Alternators – Jim Smart @Motortrend

How to Identify and Select Ford Alternators – Jim Smart @Motortrend


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, 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 Alternator

Alternator 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.

2G Alternator

The 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

3G Alternator

Ask 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.

4G Alternator

The 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 Alternator

The 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

Read on for more detail

How to rebuild a vintage General Motors alternator – Rocky Rotella @Hemmings


When a hobbyist opens the hood of his or her vintage vehicle, the alternator generally isn’t what’s admired most. In fact, short of a charging system issue that forces action, the belt-driven voltage generator is so reliable that it can operate inconspicuously for years without maintenance. Nothing underhood is truly maintenance-free, however, and our Pontiac’s alternator proved just that. It wasn’t a charging issue that drew our attention. Instead, a persistent chatter at idle speed indicated something was amiss. A cursory check revealed that an internal bearing was beginning to fail, and without swift action it could leave us stranded.

For our ’76 Firebird’s 80-amp 10SI-series alternator, bearing replacement requires removal and disassembly. After disconnecting the battery and removing the alternator’s drive belt, electrical connections, and mounting hardware, it simply lifted out and away. On the workbench, we used a 15⁄16-inch wrench and 5 ⁄16-inch hex-wrench to remove the cooling fan retaining nut and lock washer, the fan, and its shaft spacer.

Our ’76 Firebird was originally equipped with a 10SI (or System Integrated)-series alternator developed and produced by GM’s Delco-Remy division in a variety of sizes and output ratings. While remanufactured 10SI alternators are typically stocked at local parts stores, we find originality important and decided to completely disassemble our Firebird’s original 80-amp unit and replace its shaft bushings. That then afforded us the opportunity to replace the internal electronics, essentially resulting in a complete alternator rebuild. Follow along to see how we did it.

A 3⁄8-inch socket was used to remove the four through-bolts that secure the alternator case halves together. The alternator assembly was then separated by lifting the halves apart.

Read on

Belt Up!!


1 / 7


My new fan belt arrived on Saturday morning but the weather was bit a rubbish, so I began work on the Alternator today. After finding more bad workmanship around the pulley alignment I eventually got everything in place, but to my disappointment I found that the standard Model A fan belt is a few inches too long meaning that it will rub the radiator hose. So the search for a belt goes on….

Alternator Update


2 / 6

As mentioned in my previous Alternator post I called Nu Rex in the States and they were very friendly and helpful.

They advised that I’d have to split the Alternator to be able to tighten the belt pulley which in turn locks the fan pulley in place. It’s apparently very rare for one of the pulleys to come loose. I’m wondering if the clearly incorrect fan belt was part of the issue?

Nu Rex advised that the centre of the belt pulley should not be shiny if the belt is the correct item or not worn out,  as you can see we were wide of the mark on both counts!

I was also advised that the standard Model A Fan Belt is the correct item, and also to re black the pulley with a marker, which once it becomes shiny again will indicate belt change time.

Popped up to Simon’s and both he and his Dad gave me a hand to tighten the pulley and also lent me a piece of welding rod to lock the brushes in place to allow reassembly of the unit.

Correct fan belt was ordered and has been delivered from the ever reliable O’Neill’s Vintage Ford

Weather permitting I can get the unit refitted tomorrow

I’d like to get back mobile as there is a car rally/breakfast event at the nearby Wellington Country Park Farm Shop on the 11th September.


First Day Road Legal & Tidying Some Wiring


3 / 8

4 / 7

The Sport Coupe is all registered and UK road legal, a lot of work to do yet but getting there.

Temporary plates whilst I wait for the nice US style ones I’ve ordered from Miles at Jackhammer Speed Shop.

My Wife kindly helped cut out some hardboard for us to stick the vinyl temporary ones on 🙂

Did some under bonnet wiring tidy up today, fitted a new conduit and wires removing the some more of the fire hazard stuff!!

Had a visit from a colourful  interested party along the way 🙂



Triumph Herald Alternator Conversion (originally published in 2008)


So it begins, out with the old and in with the new(er)

Started with removing the dynamo (strangely enough:-))

Please note that the dynamo may foul the distributor.

Got around this by loosening it off and turning it away from the dynamo.

Be sure to mark the position of the dynamo before loosening so as not too put the timing too far out.

I put a small felt tip pen mark on an HT lead to line up with the LT lead of the distributor.

The dynamo was then removed.

Tried a few test fits of the altenator with the various parts of the existing dynamo bracket.

It would appear the best way to do this is to remove all the existing bolts etc (including the large one in the alternator and dynamo picture above) and replace them with two different size bolts and a large amount of washers to ensure all the pulleys line up.

The Herald fan belt will also now be too short, I’ll pick up an new one when I get the bolts.

Herald Update (originally published in 2008)


I have purchased an alternator for the old girl, and will shortly be fitting it and converting to negative earth at the same time.

Got a very good deal on the alternator, eBay of course!

I’ll publish the trials and tribulations of the conversion here in the future.

It looks as if only the heater blower, tank sender, battery and ignition coil will need reversing during the process, I think???