3G Alternator Upgrade
swap-in a '94/95 5.0L GT 130A 3G Alternator
into an 86-93 5.0L GT/Cobra.
Text and Graphics (C)1997 Byron
permission from http://cobra.tvi.com/altproj/3g.html)
Text and Graphics
(C)1997 Byron Reynolds ([email protected]) Reproduction for
PRIVATE USE permitted. Any other use requires written
permission from the author. Disclaimer: This information
is for entertainment purposes only. The author provides
this information free of charge and without warranty or
support. The author believes the instructions contained
herein to be correct. He has performed this procedure on
his own vehicle with success and has road-tested the
solution for 1200 miles before releasing this
information. Use this information at your own risk.
1993 Vibrant Red SVT Cobra
If you don't currently
have a problem, this upgrade offers you nothing. However,
I've been exposed to dozens of stock Mustangs and nearly
all of them have charging problems at idle. You may want
to read this project , run some tests, and decide for
Connect a volt meter
to the terminals of the battery in your stock 86-93
Mustang. Run the car at idle, and watch the voltage dip
below normal battery voltage level (as low as 10 or 11V)
when the lights and heater are on. It should soon become
clear why Police Special Service Mustangs were equipped
with more powerful alternators. If a stock Mustang is
left at idle with the headlights and heater on, the
battery will be dead within a few hours.
This popular add on
has an unfortunate side effect, it amplifies the
electrical problems stated above. Underdrive pulleys
reduce the speed at which the alternator spins. If you're
running underdrive pulleys, have a stock 75A alternator,
and are idling at factory 650 - 750RPM idle, your battery
is probably being discharged. Add lights, heater fan,
rear defroster, and a big stereo to this scenario, and
your battery is definitely in trouble. To fix this
problem, people commonly bump up the idle speed to around
1000 RPM or more. This brings the alternator back up to
stock speed, but ruins stock idle, wastes fuel, and
causes problems in some states with tight emissions
The factory alternator
uses a 3-prong spade connector. Two of the spades share
the current coming from the alternator. These terminals
often wear/corrode and cause a resistive electrical path
for the current to flow. The resistance causes heat;
enough to melt the connector, create a short circuit, or
start a fire. If you've ever replaced the factory
alternator, you probably noticed that it came with a
fresh connector and big warning labels describing the
dangers of not replacing the old connector with the fresh
one. This problem is well known, and the cause of
numerous alternator failures, engine fires, etc. The 3G
130A alternator does away with this problematic
Stronger Is Better:
Running a 3G 130A
alternator at 30% capacity is much better than running a
75A alternator at 60% capacity. A 3G alternator will last
a long time when put on "light duty" use in a
Mustang. This alternator is made to run winches, light
bars, spotlights, etc. It has a tough diode pack and
voltage regulator, improved bearings, etc. It's twice the
alternator at only 25% additional cost.
The 3G unit looks
Internal cooling fan,
modern design, clean and mean.
Get to know the 3G
A picture of this new
alternator can be seen below. Note the differences
between it and your factory 75A unit.
The 3G model
alternator feeds power through a high-power electrical
terminal instead of the problematic spade connectors in
the 75A model. The stator signal wire is located on a
separate connector on the 3G model. Because of these
differences, the stock wiring harness will need
modification before the 3G alternator can be put to use.
The mounting holes on
the 3G are in the exact same location as the 75A model.
However, on some models, the top mounting hole is not
threaded. It is necessary to use a nut, bolt, and two
washers at the top mounting location.
There can also be a slight clearance problem requiring
modification of the alternator bracket. It may be
necessary to trim a triangular section of the bracket in
order to make room for the larger 3G alternator. The
modification is minor, easy to accomplish, and does not
adversely affect the strength of the bracket. I have
heard reports from several people that have done this
install who state that clearancing was not required due
to variations in bracket designs.
Also, be forewarned, if you have a Powerdyne BD-1x
supercharger kit on your Mustang, you will need to
fabricate a small extension bar to pivot the alternator
further away from the smog pump or it will contact the
smog pump housing and destroy it (learned this the hard
way). Also, you'll need to get a slightly larger
serpentine belt to make things fit. A 910K6 belt works
well. Reports in from the Vortech crowd say that there
are no clearance problems with that kit, but this has not
The pulley is larger. The alternator that this author
purchased came with a pulley slightly larger than the one
found on the 75A model. It's about the same size as the
pulley that came with an AutoSpecialties underdrive
pulley kit that was already installed on this vehicle, so
there was no need to change it. If this pulley is
retained on a vehicle with stock pulleys, the stock
serpentine belt should still fit, but it may be a bit
tight. The pulley can be changed if the smaller stock
pulley is desired.
(1) 130A 3G alternator. Mine was purchased from Pep Boys
It was specified as standard equipment for a '94 5.0L
(1) 2" Grade 8 3/8" coarse thread Bolt (29
(1) Grade 8 Nut for above (10 cents)
(2) Washers for above (20 cents)
(1) 10" length of 10 or 8 gauge stranded-core
electrical wire. (20 cents)
(1) FORD 3G Alternator stator wire connector (Junk yard,
(1) Electrical screw lug connector (10ga) (10 cents)
(1) 12" length of 1/2" diameter wire loom. ($2)
(1) 2" section of 8 gauge heat shrink tubing (10
(1) 2" section of 14 gauge heat shrink tubing (10
Socket set, Wrenches,
Electrical pliers, Soldering Iron, Solder, Voltmeter (for
testing). Dremel, Die Grinder, or equiv. (if bracket
clearancing is needed.)
mechanical and electrical experience, this entire
procedure should take less than 2 hours to perform. The
author completed the install the first time in about 2
hours and the second time in approximately 45 minutes.
Prep the car:
1. Start by
DISCONNECTING THE BATTERY and removing the serpentine
2. Unplug the factory alternator connectors from the
3. Unbolt and remove the factory alternator (2 bolts).
4. Tie top radiator hose out of the way.
5. Remove air filter housing and filter to give more room
to work. (optional / recommended)
6. Peel back / unravel plastic covering on factory wiring
1. Test fit the 3G
alternator, slide in the bottom mounting bolt, and rotate
into position. If you have a supercharger kit installed,
these instructions will not make sense but may be of some
2. Mark the factory alternator bracket needing clearance
3. Clearance the alternator bracket by cutting/grinding
away the marked area with a die cutter or dremel. The
author used a dremel and a small cutting bit. This part
took about 10 minutes to complete.
4. Secure alternator using original bottom bolt and new
2" top nut, bolt, and washers.
1. Locate the point
where the pair of MAIN wires (black/orange) join and
2. Cut at intersection., leaving one MAIN wire.
3. Splice in new piece of 10 Gauge wire, solder, and use
heat shrink tubing to insulate.
4. Test fit wire to alternator MAIN lug, trim as needed
for good fit.
5. Crimp and solder on screw-terminal, use heat shrink
tubing to insulate as needed.
6. Install screw lug on MAIN screw terminal. Once tight,
slightly bend screw lug away from alternator housing.
7. Cut stator wire 2" from factory oval plug. This
cut frees the factory 3-prong spade connector which can
8. Splice in new stator connector, solder, use heat
shrink to insulate.
9. Apply wire loom, plug in connectors, tie wrap as
1. Re-install air
filter and housing.
2. Reconnect battery and immediately check voltage across
terminals. It should read above 12V. If not, disconnect
battery and check installation.
3. Untie radiator hose.
1. Connect voltmeter
across battery terminals.
2. With key off, voltage should read 12-12.6 volts. My
car was at 12.4V.
3. Turn off all accessories and turn key on.
Instrumentation battery light should be on (dash). And
voltage should drop to between 11 and 12V.***if voltage
drops below 10V, remove key immediately and re-check
4. Start car. Voltage should jump to above 13 Volts. Our
car was at 14.2V. Battery light should turn off.***if
this does not happen, shut off car immediately and
5. Bring engine to 2,000 RPM With all accessories off,
Voltage should be above 14V. Ours was at 14.4V.
6. Return to idle. Voltage should still be above 13V.
Mine was at 14.2V.
7. Turn on headlights. Voltage should still be above
12.5V. Mine was at 14.2V.
8. Turn heater fan on high. Voltage should still be above
12.5V. Mine was at 14.1V.
9. Turn on road lights. Voltage should still be above
12.5V Mine was at 14.0V.
10. Bring engine to 1,000 RPM. Voltage should be above
13V. Mine was at 14.5V.
11. Shut off car.
Congratulations, you have greatly improved your
electrical system and can look forward to longer battery
life, improved charging at idle, and plenty of power for
even the most demanding electrical accessories. The
authors vehicle can run the headlights, fog lights,
heater fan, rear defroster, window wipers, brake lights,
and a 250W 10 speaker stereo system...with the car at
idle... without causing the improved electrical system to
dip below 12.7V. Even with all these accessories on, the
battery is still being charged!
The Corral: Late Model
and text © Copyright 1998 The Corral.
All Rights Reserved, Duplication Strictly Prohibited.