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Ford Alternator Upgrade for More Battery Charging Power

Posted in How To: Electrical on December 20, 2016
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It’s cold. It’s dark. It’s raining. Your reach down and flip on the fog lights. They help but not that much. So you power up the light bar. Yup! That’s the ticket. The stereo is cranked up and life is good. Well, until you look at the volt gauge needle sitting in the red zone on the downhill side of 12. Not good.

That’s life when you’re driving a truck built in the automotive electrical stone age of the ‘70s through the early ‘90s where alternators had an amp output the same as most highway speed limits of the time.

A quick history

During that time Ford used three generations of alternators in trucks. The First generation was dubbed the 1G (1973-1986), which had an external regulator and produced 40-65 amps. Its output was sufficient for a stock F-Series or Broncos, but add accessories and it just didn’t make the grade for most off-roaders.

The 1G was upgraded in 1986 with the second-generation “2G” that used an internal regulator for a more efficient unit that put out 60-70amps. The problem is the 2G was a headache for Ford: It required an additional side-wiring harness and the plastic power plugs were prone to falling apart, the spade terminals working loose, shorting wires and causing fires.

So when the new 1992 F-150 (last generation Bronco) came out, Ford rolled out the 3G that brought both 95A and 130A versions to the battery-charging party along with several case configurations to fit a wide range of both cars and trucks.

The huge upgrade of this alternator over the 2G is a self-exciting, externally regulator that only required one cable between it and the battery to complete the circuit. Clean, simple and powerful.

It also worked with the no-charge idiot light, making it an ideal replacement for rigs running the older alternators – and for those Ford owners wanting to run extra lights, bigger sound systems, winches, plows and other aftermarket accessories.

Powermaster’s 200-amp Ford large-case 3G alternator (left) is slightly larger in diameter than the stock 2G (right). The 3G is a direct upfit replacement for the 2G in 1987-’96 F-Series and Broncos.

Why 3G upgrade?

3Gs come in two sizes: A a 7-inch “small case” and an 8.25-inch “large case.” Both can be found in 95- and 130-amp versions. The 95-amp model is easily identifiable by three sets of four round cooling holes in the case’s ribs that make a “Y” behind the pulley. A 130-amp high-output version uses three sets of two big cooling holes in the “Y.”

It’s not unusual to find 3Gs in pick-your-parts boneyards that put out 90-100 amps at idle and up to 160 amps at highway operating speed. The high-output 3Gs are interchangeable in vehicles that already have a factory 3G as long as the mounting patterns (two-ear, three-ear, side- and pivot mount) are the same.

That’s what makes a high-output 3G a great upgrade for any Bronco or F-Series owner running either of the alternator’s predecessors. In stock form it will provide two to three times more juice than the 1G/2G alternators and is far less likely to overheat under heavy current draw. The 3G can also run either a v-belt-style pulley or serpentine-belt pulley while fitting into those older mounts with very little effort.

The 2G uses two plugs for wiring whereas the new 3G simplifies wiring with only a single 4AWG (or larger) cable needed between the battery, starter relay and the alternator’s output post (top).

A simple swap

The alternator shops I spoke with say the 130-amp version can be found in both small- and large-case 3Gs. However, the latter is the only one that can support higher outputs, such as the Powermaster Performance 3G 200 that we are swapping in to replace the wimpy 65-amp 2G in our ’91 Eddie Bauer Bronco.

We found the diming of our Bronco’s headlights and slowing down of wipers when we powered up a few lighting accessories totally unacceptable. With our goal of adding a winch and 12V on-board air system in the very near future, along with more lights, it was time to put some real muscle in our old rig’s electrical system.

We turned to Powermaster Performance for advice. Powermaster is well respected in the off-road and racing industry for their top-shelf starters and alternators. JR Richmond, one of Powermaster’s lead techs, asked what we had in mind for electrical accessories and then suggested we swap out the OE 2G for their 200-amp large-case 3G (#477711). He also recommended we have them “clock” the case so the charge post is at the 6 o’clock positon to place the wiring in the same position as it was from the factory. We did both.

In our case the swap was as simple as removing the old 2G and tossing the wiring harness. Then we did some very minor trimming on the aluminum alternator bracket, bolted on the Powermaster 200-amp alternator, and ran a 4ga-charge cable through a 200-amp MEGA fuse to the solenoid mounted on the fenderwell. The final step was routing a 4ga cable to from the fusible link to the positive post of the battery. That’s it.

The charge indicator light on the dash works and now the Bronco voltmeter needle stays steady a shadow over 14 volts no matter what accessories we turn on. When you have an alternator that cranks out 139-amps at idle, 165 at cruise, and 210 on the top-end, it’s no surprise to see voltage remain unfazed with what we are powering at this time. We expect similar performance when we add LED lights and a few other goodies down the road.

A quick way to tell the difference between a 95-amp 3G and a 130-amp (or higher) version is the latter has two large holes in each of the three legs of the “Y” on the front of the case. A 95-amp model will have four smaller holes in each leg of the “Y.” This is the Powermaster 200-amp “large-case” 3G.

Budget 3G Swap

Those on a tight budget that want to do a H.O. 3G upgrade can find them in a number of cars, trucks and vans in the mid- to late ‘90s. Here’re suggestions for sourcing a “pick-and-pull” high-output 3G:
• 1966-1986 all engines use a 8.25-inch (mounting ear spacing) pivot-mount, V-belt 2G alternator; good donor vehicle is alternator from 1991-1992 non-DOHC Taurus’
• 1987-1997 4.9L (300)/7.5L (460) engines use 8.25-inch pivot-mount, V-belt alternator; good donor vehicle is alternator from 1991-1992 V-6 Taurus sedan/wagon
• 1987-1992 5.0 (302)/5.8L (351) engines use a 7-inch pivot-mount, serpentine-belt 2G alternator; good donor vehicle is 1993-1996 4.9L E/F-Series Vans or 1994-2000 V6 Mustangs
• 1993-1996 5.0 (302)/5.8L (351) engines use 7” side-mount, serpentine-belt 95-amp 3G alternator; good 130-amp donor vehicle is 1996-1998 4.0L V6 Explorer

Note: Usually a 1G/2G to a high-output 3G swap requires slight mounting bracket clearancing due to its larger case and the use of a pigtail adapter or minor wiring modification. A 95-amp 3G swap to 130-amp 3G is plug-and-run. Use 4AWG (or larger) charge cable/grounds and MEGA fuse when upgrading to a 130amp or higher-output alternator.

Some 3G top 3/8” mounting holes (left) are smooth bore, unlike the threaded OEM 2G’s mounting hole like this one we pulled off of our ’91 Bronco’s 302.
Upgrading to the 3G only requires replacing the short, threaded OE top mounting bolt (left) with a 3/8”x2” bolt with flat and lock washers as shown.
The factory alternator mounting bracket for 1G/2G alternators typically requires removing a little material from the bottom and middle gussets, and from the underside of the top mounting hole to make room for the slightly larger 3G case.
Our installer, John Hagan, uses a carbide grinding burr on a compact ¼-inch 90-degree air drill. It works like a charm in the tight confines to quickly trim down the aluminum for the needed clearance.
Powermaster highly recommends using at least a 4AWG charge wire when stepping up to 130-amp or higher output alternators.
This plastic plug is one of the prime “failure” points of the Ford 2G alternators. The stock 2G wiring harness can be either taped and tied off in case you want to go back to the original setup later on, or be remove completely. We did the latter because our new alternator didn’t require incorporating any part of the old wiring.
John says this was the easiest 2G-to3G swap he’s ever done. The Powermaster we used only needed a new 4AWG charge wire, run from the alternator to the starter relay on the fender, to make it work.
We placed a Littlefuse 225-amp MEGA fuse in line between the alternator and the starter relay on the fender of our ’91 Bronco. Always use a fuse that’s rated 10-15 amps higher than the alternator’s output.
The installed Powermaster 200 fits like it was that way from the factory. It provides three-times the amps that the OE 2G produced at idle, which is great for off-roading.
Every unit shipped from Powermaster is bench-tested. Our unit passed with flying colors. Note the idle (139amps) and cruise output (165 amps) numbers. That’s slinging some healthy juice to the battery!
Running LED light bars and other auxiliary lights create a big load on a rig’s electrical system so its important to have an alternator that’s up to the challenge. A 130-amp (or higher output) 3G is a good choice for owners or early F-150s and Broncos.

Amp Draw

Plan out the amp draw accessories put on your alternator before ordering. These ballpark figures are done using OHM’s law where Amps=Watts/Voltage. Voltage varies from around 12v to 14.7v depending on the engine rpm and the output of the alternator. For example, a 300-watt double-row LED lightbar would draw 23.8 amps at 12.6 volts, or 21.1 amps at 14.2 volts. Here’s a general overview of accessories and amp draws based on a 12-volt power output:
6 LED Fog Light: 2-3 amps
10” LED Lightbar: 5-6 amps
40” 300W LED lightbar: 21-24 amps
H11 55Wx2: 10-15 amps
HID 55Wx2: 6-8 amps
Xenon 35Wx2: 14-20 amps
H3 100W Spot Light: 8-10 amps
12v Air Compressor: 20-50amps
10,000-pound-capacity winch: 380-470 amps
CB Radio: 1-2 amps

Installation Tips

The key to getting the maximum performance from a 3G alternator upgrade is making sure you don’t take shortcuts in an effort to save time or money. Here’re a few tips from Powermaster Performance’s JR Richmond along that line:
• Use at least a 4AWG charge wire between any 130-amp-plus alternator and battery; using a smaller diameter wire creates too much resistance that can overheat and/or damage the charging system
• Keep the charge wire as short as possible to maximize alternator performance.
• Use a fusible link [MEGA Fuse] at least 10-15 amps larger than the alternator’s maximum output.
• Ground the alternator housing if the brackets have any coating such as paint, powder coat, chrome or anodizing.
• Solder, don’t crimp terminal ends. Loose terminal ends from poor crimps are a big issue.
• Tighten belts. Slipping belts on manual tensioner systems, like those used on V-belt systems, generates a lot of heat that will transfer into the alternator, causing it to fail. (Over-tightening a belt will not affect a modern alternator’s bearings.)

Amazon Affiliate links are our attempt to show you real-world pricing and availability for the products we review and install, and while the Amazon links are separate from editorial and advertising, the Four Wheeler Network may receive a commission on purchases made through our posts.


Summit Racing
Akron, OH
Powermaster Performance
West Chicago, IL 60185

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