Ford F100 3 Wire Alternator Wiring Diagram
| How-To - Interior and Electrical
How-to Install a High-Output Ford 3G Alternator into Older Fords
Charge Into the 21st Century with Ford's Late-Model Alternator
Introduced in August 1964, Ford's first-generation Model 1G alternator was a real step up in reliability and current output compared to the old-school generators it replaced. Originally available in ratings ranging from 38 through 60 amps, the 1G was at best barely adequate when the electrical system was brand new and most cars only had a radio, a heater, windshield wipers, lighting, horns, and a points ignition system. But with an aging, under-wired electrical system and today's typical hot rod add-ons like electric fuel pumps, fuel injection, high-output ignition systems, Halogen headlights, power windows, and air conditioning, those lazy 1G alternators and their crude separate voltage regulators aren't up to the job. Frankly, other than a straight resto, it's time to put them out to pasture in favor of modern, high-output alternators with internal regulators.
For many years, a popular solution for old Ford vehicle owners that needed more amps was adapting an integrally regulated GM alternator for use on a Ford. GM climbed on the high-output, integrally regulated alternator bandwagon far earlier than Ford, introducing its reliable, first-generation "10-SI" alternator as an option on some cars in 1969 before it became standard equipment on all of the General's vehicles by 1973.
Playing catch-up, Ford didn't come out with its first integrally regulated alternator until 1982, when the model 2G alternator appeared. The 2Gs were offered stock in 65- and 75-amp ratings, but they had reliability issues even in bone-stockers.
In 1994, Ford finally hit a home run, introducing the 3G integrally regulated alternator that remained in use on some Ford vehicles well into the 21st century. Up to 200 stock amps are available with some variations; 130-amp versions exist that still have directly opposed mounting ears that permit them to physically bolt right into place of that old model 1G using the existing 1G brackets. Highly reliable and easily adaptable, the 3G has become the go-to alternator for Ford retrofitters.
Let's take a closer look at the 3G, as well as what it takes to perform a quick, typical retrofit into a 1960s classic Ford, courtesy of Advanced Engineering West's Mark Sanchez. We'll be using quality AutoZone-remanufactured alternators, plus a late-model Ford OE 3G harness scrounged from the wrecking yard. Sanchez's preferred method of wiring the 3G up just like a Ford stocker lets you go to any auto-parts store for a replacement if the alternator takes a dump on a long-distance cruise—something you can't necessarily do with those universal one-wire alternators.
Which 3G?
"All amped up and ready to go where no old Ford has gone before, Ford's 3G alternator is easy to swap into older Fords. "— Mark Sanchez, AEW
For both 1G V-belt and most 2G serpentine-belt conversions, you want a 3G alternator with case mounting ears that are 180 degrees opposed (straight across from each other), with 6.900-inch bolt centerline spacing. Other 3G variations with offset ears or ears on one side of the case won't work as direct replacements. One 3G alternator configuration meeting this requirement was originally installed on 19941995 Mustang V8s, 19941997 Thunderbird/Cougar XR7 3.8L V6s, and 19942000 Mustang 3.8L V6s. AutoZone's remanufactured Duralast unit for this application is PN DL7734-6-11. Unlike sketchy wrecking-yard take-outs, AutoZone's Duralast alternators carry a lifetime warranty.
Reclocking
It's a better than even chance the new alternator case shells will require reclocking so the connections end up in the right orientation for your specific installation. Both early and late Ford cases are held together by three bolts, so there are three possible clock positions. For the Ford-style alternator, we'll define the clock position as "read" looking from the rear of the case forward. The amount of "clocking" is the offset in imaginary old-style analog "clock hours" between the case's small "adjuster ear" and the battery-stud terminal and/or main connector, with the small adjuster ear facing straight up ("12 o'clock"). What's a little confusing is that on most classic Ford muscle cars, the 1G alternator adjuster ear faces straight down as installed on the stock brackets, while on the 180-degree-opposed 3G late-model stock serpentine-drive installation, the adjuster ear mounts straight up—but we need to define a common reference point to determine the reclocking amount needed (if any).
For the 1966 Galaxie 352 shown in the photos, the new alternator's clocking was way off as delivered, but correcting it was a cinch: Unlike GM-style alternators, the internal brushes on Ford units are unlikely to fall out when separating the front and rear shells as long as the center black ring element doesn't pull away from the rear case shell.
Reclock a Ford alternator by removing the three bolts holding the case together. Carefully separate the front case shell from the black ring and rear shell, then rotate the shells as needed (top). A small prybar may be needed to start the separation process, but be gentle! If the large, long mounting ear for the -inch through-bolt prevents the necessary amount of rotation needed to reach the correct clocking position (bottom), gain additional separation clearance by removing the front pulley and pulling the front shell further forward.
Pulley Swaps
Late-model 3G alternators come equipped with serpentine-drivebelt-compatible pulleys, but the old Galaxie uses V-belts. We found that the V-belt pulley fit properly on the 3G's supposedly metric shaft, aligning perfectly with the car's other pulleys.
Other Parts Needed
Hooking up the new alternator requires complementary wiring that matches the new alternator's configuration and output, including late-model connectors and the proper 4- or 6-gauge positive battery (B+) charge wire. The original 1960s charge wire was usually only 12-gauge and, at least on the 1966 Galaxie shown here, wasn't protected by any fusible link. The plugs and upgraded wiring are part of the junkyard 3G alternator harness, which costs about $7 at the local Pick-A-Part yard. Any 3G alternator harness works; you don't necessarily need one that specifically matches the recommended Mustang alternator configuration.
Want to build your own harness instead? Del Mar Wiring is one source for the correct 3G-type connector and pigtail assembly. Sanchez at AEW has original Ford connector bodies and terminals if you want to start entirely from scratch. Due to the 3G alternator's high output, use AWG-4 or AWG-6sized wire protected by dual 14-gauge fusible links or a 150- or 175-amp mega fuse for the main alternator "BAT" stud charge-wire running back to the starter solenoid.
Sanchez usually grabs a complete alternator rear harness from any 3G-equipped Ford in the wrecking yard. The harness includes the proper connectors, fusible links, and wire-gauge sizes for every cable. The plain green wire visible in the bottom photo came with this particular takeout harness, but isn't used or terminated on typical retrofits.
No Run-On
One problem with GM alternator conversions is that most GM OE-replacement-style units need a diode or resistor spliced into the wiring if not running an idiot light. Otherwise, due to current backflow, the alternator remains energized and the engine keeps running, even when the ignition key is turned to the "off" position! That's because, on the GM system, the warning bulb also supplies the necessary resistance to shut down the system and avoid backflow.
But this isn't an issue with Ford alternators. You can run any combo of idiot light, voltmeter, or ammeter without run-on problems. It's true the stock Ford idiot light circuit behind the dash has always had (depending on the model year) a 500- to 560-ohm resistor in parallel to the bulb, but not running the resistor only causes the bulb to not turn off (it does not affect alternator shutdown). However, we don't recommend running an ammeter because of the 3G's high output; convert to a voltmeter instead.
Gain, No Pain
You can upgrade from a 60-amp (at best) 1G alternator to a modern, reliable 3G 130-amp alternator for around $50 (using a wrecking-yard alternator) or just under $200 (including a quality remanufactured alternator). Even if your vintage ride doesn't normally demand a full 130 amps, the late-model alternator can—when required— generate 540 percent more amps off-idle (81 amps versus 15 amps at 900 engine rpm). You'll appreciate that on a cold, stormy, dark night with your brights, heater/blower, and windshield wipers all running full blast. An alternator only generates the amount of amps when conditions require it, so having a huge "reserve" capacity that's rarely used should reduce the unit's duty cycle, extending its useful lifespan. It may outlast the car.
Ford/Motorcraft Alternator Lineage
1G: 19641986
Ford's original, separately regulated, alternator design, production versions were officially rated at 38 to 60 amps, although higher-output aftermarket versions are available.
2G: 19821993
Ford's first integrally regulated alternator, originally produced in 65- and 75-amp models. Corrosion and resistance buildup in the power-wire connector caused high failure rates.
3G: 19942008
This integrally rated unit makes for the easiest retrofit into earlier vehicles. It corrects all of the 2G's faults and uses internal fans for improved cooling. Use those 3G variants that still have 180-degree-opposed mounting ears to replace earlier 1G and 2G alternators. The 3G alternators are available stock in 95-, 130-, and 200-amp ratings.
4G: 19962007
The fourth-generation design includes several different case configurations, including the "pancake" version used with 19962002 Ford Mustangs equipped with Modular V8 engines. Very compact, it came stock with 150- and 200-amp ratings. No versions have 180-degree opposed mounting ears, so custom brackets would be required to use it on earlier engines and vehicles.
6G: 1999present
First used on some 1999 Mustangs and Crown Victorias, it can be found on the 20022004 four-valve Modular motors, 2005-and later SN197 Mustangs, and many other late Ford cars and trucks. It's available in 130-, 170-, and 200-amp ratings, but unique mounting ears make it hard to retrofit.
Source: https://www.motortrend.com/how-to/install-high-output-ford-3g-alternator-older-fords/
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