3G, 130A ALTERNATOR UPGRADE

There is a potential problem with splicing in 10AWG wire as directed in the Corral tech article (Byron Reynolds' 130A 3G Alternator Upgrade) and in the article in MM&FF, entitled "Current-cy Exchange" (Nov. 1999) to which I responded with a letter that was published in the Jan. 2000 issue.

The Problem

The pair of black/orange wires that join and become a single black/orange wire are all the same wire gage (10AWG). The single black/orange wire joins a 14AWG fuse link before connecting to the starter relay on the same stud that the positive side of the battery is connected to through the 4AWG battery cable. The single black/orange conductor and the 14AWG fuse link are not large enough to handle the potential current that could be supplied from the 3G 130A alternator. It was barely large enough to handle the output of the 2G, 75A (more like 60A) alternator. Also, when using fuse links, they are to be 2 sizes less than the conductor they are protecting.  I'm told some years do not even have a fuse link but I cannot verify that; it seems unlikely since this wire must be overcurrent protected.

The maximum standard load is 50A which includes all exterior and interior lighting, turn signals, radio, A/C blower fan, fuel pump, wipers. Intermittent load (power windows) would add to this but are not significant since they are short duration. Add to this a secondary electric fuel pump (see current draw on my Walbro Pump Data page) and electric cooling fan, a high power stereo and you could have a continuous load of 90 amps or more. The standard wire that Ford uses is only a 10AWG which the National Electric Code Ampacity Tables (see excerpt below) rate at 55A. It's barely able to handle the normal load, let alone an 80A load. Using this existing wire could result in a potentially dangerous situation, if not now, then in the future after many heating and cooling cycles. When the vehicle is running and the battery is near or at full charge, all the current supplied to the vehicle comes from the alternator and is flowing through the single black/orange 10AWG wire. Given that the 3G alternator has the capability of significantly overheating this wire, I would recommend paralleling or replacing the original wire with 4AWG wire. If you rely on the stock wire alone and it does overheat, it will melt all the wires running adjacent to it.

The Solution

Refer to diagram below, "12 - Charge/Power Distribution".  SSave to your disk drive and zoom in to read the notes.

I felt it was easier and cheaper to run new wire. I used 4AWG battery cable with lugs pre-attached (since it is inexpensive) and an in-line high amperage 12V fuse and holder, available from E&B Marine or West Marine.  The reason for the fuse is if one of diodes inside the alternator ever fails, the resulting direct short across the battery would burn up the 4AWG cable and possible start a fire.  For the same reason, Ford protected the black/orange wire with a green fuse link.

You can use a 125-150A fuse.  I chose the 125A  because fuses should be sized to protect the lowest rated component in the line.  In this case, the alternator is 130A and the 4AWG is 136A.   Also, fuses do not blow at their rated value.  The time it takes it to blow is depends on the current flow as a percentage of the fuse's rating.  At 140% (175A) of this fuse's rating, it will take it 200 seconds to blow.  At 180% (225A), it will take 6 seconds; at 280% (350A), it takes 1 second.

Leave the existing spade connector, splice into the stator wire (White/Black) with the new stator connector.  The White/Black wire loops through the harness from the oval connector to the rectangular connector.  This is shown on the wiring diagram near the end of this page.  Use an interlock connector (see picture below) to splice on to the stator wire.  My battery is on the passenger side, next to the alternator so the cable lengths are different from standard. Get 2 battery cables (4AWG is what they had, it's overkill, but only $3 per 18" cable, with lugs on both ends). Your lengths will depend where you mount the fuse holder. Run one from the stud connector on the alternator (you'll have to crush it slightly side to side to make it fit within the stud's plastic insulator) to one side the fuse holder. Route the second wire from the other side of the fuse holder to the positive side of the battery. In this configuration, you could still use a 2G alternator because you haven't cut off the connector but you are no longer using the marginal 10AWG black/orange wire, but 4AWG battery cable.

DO NOT remove the existing 10AWG black/orange wire (connects to a green fuse link) from the starter relay.  The yellow/white wire (connects through a brown fuse link) connects through the green fuse link and is needed for proper regulator control.  By removing the black/orange wire, you have disconnected the yellow/white wire from the battery.  See the paragraph on "Alternator Basics" below.

Interlock Connector

The Fuse

The fuse can be obtained from the following source: Wilde EVolutions.com, http://www.wilde-evolutions.com/ MEGA Fuse Holder:                        Item#: FU5520     Price: $9.65 MEGA Fuse (150 A, 32VDC):       Item#: FU9523     Price: $5.90 (Littlefuse brand Mega fuses, 100 to 250 Amp with 32 VDC rating).

You can also obtain these items from your local West Marine store.

When is a 3G not a 3G?

As an aside, not all 3G's are 130A, some are 95A and some are 105A, as 3G's are used on many different vehicles. Basically, the 3G's have the internal cooling fan instead of the external fan used on the 2G. The 3G also uses a stud for the charging wire instead of the spade connectors on the 2G.   Also, there are probably 20 different mounting varieties of 3G's.  The correct 3G has the mounting ears spaced 175mm apart, 180° from each other.  Also, the standard pulley for the 3G is 60mm.  The 2G pulley is about 50mm.  If you have a lot of current draw at idle (i.e., Lincoln Mark VIII electric fan: 40A at idle), get the Auto Specialties 1 3/4" (44mm) pulley shown below.  The 3G for the Mustang is 130A and is exactly as shown below.

NEW INFO!

If you do not get enough ouput voltage at idle, replace the standard 60mm pulley with a 1 3/4" (44mm) overdrive pulley from Auto Specialties.  It's easy to monitor voltage on the go, make a cable that connects your DVM to the cigarette lighter and watch it under all conditions. The voltage will drop off when the engine/alternator get warm; this is normal.  When the load increases, i.e. electric fan comes on or you turn the AC/heater blower on, the voltage will normally drop.  It would be nice to keep the voltage at idle above 12.6V, which is the voltage of a charged battery, otherwise you will be drawing currrent from the batter (discharging it) instead of from the alternator.

Auto Specialties Performance
13313 Redfish, #104
Stafford, TX 77477
(281) 261-5811
(281) 261-5715 Fax (281) 261-5811
Order Toll Free "24 / 7" 1-877-928-8678

84-96

4.3, 305, 350, 454

1 3/4" Overdrive Alternator

ASP520004 $19.95

Here is a list of vehicles that have the 3G alternator, most are 130A, but some might be 110A:

94-96 Mustang 3.8 V-6
94-95 Mustang 5.0
94-96 Thunderbird 3.8 V-6 (non SC)
95-96 Windstar 3.0 V-6 (most are 3.8's)
93-96 E/F series Trucks/Vans 4.9 L6*
96 Sable 3.0 V-6
94-96 Cougar 3.8 V-6

*Probably the best one if you can get it (should be easy to find, too) is off the E/F series...this series uses a threaded top ear like the stocker on the Mustang....E/F series with threaded ear uses metric bolt. ALSO, make sure the E/F series is 130 Amps and NOT 95.

This table shows that some of the alternators used in '87 were only 65A.

This table shows that all of the alternators used in '88-'93 were only 75A.

This table shows that all of the alternators used in '94-'95 were 130A.

This table shows that all of the alternators used in '96-'99 were 130A, but the 4.6L have a different mounting arrangement.

The 6 cyl are the same as the '95-'95.

Alternators and Voltage Regulators

Not all 3G alternators are created equal (see new info below). The alternators (and starters) you get from the large discounters are not high quality pieces. That's why you see people going through 2 or 3 different ones within a few weeks. The components the manufacturers use are the least expensive they can acquire and the finished units are not fully tested for a sufficient period of time. So the discounter offers a lifetime warranty, they raise the price of the component accordingly to account for the high return rate, and everyone is happy.

You can have a high quality OEM equivalent put together by a generator shop for about the same price or maybe less and they won't require a core exchange.

The Powermaster is a 2G that uses a 2G case, bearings, external fan but with a higher capacity stator and rotor. My alternator man had built a few of these for customers who wanted them, and showed me one, looked just like a 2G. For the same price, you can get a 3G with better cooling and larger bearings.

Some of these aftermarket alternators are Mitsubishi's or clones, a quality unit used on many domestic vehicles now.

AutoZone sells the Duralast brand with lifetime warranty.  Ask for 1994 Mustang 130A alternator, part number DL7734-6-11, $107.99 + $40.00 core exchange.  This price seems to vary is different parts of the country.

Any good alternator shop can put together any alternator you require from parts obtained from their normal suppliers. I suspect, that's what Anderson and others are doing. Using the best quality parts, the low volume shop's cost is about $150. Pep Boys pays way less than $100 for the unit they sell for $108 and the assembler's cost is probably less than $50.  Cost is the main factor for manufacturing these items, that's why you hear of so many failures. They can offer a lifetime warranty because the cost of returns is built into the high markup and the parts used are the cheapest they can get.  My $200 alternator was over $100 in parts!

There is also more than one type of regulator. Some manufacturers make a heavy duty model for the 3G. Transpo Electronics make a F794 and F794HD. The F794 is the OEM equivalent, the F794HD is a heavy duty model and has a lower saturation voltage which results in cooler running and a better temperature coefficient. Neither of these have a Load Response Control Circuit. Without this circuit, when the load on the alternator is increased, there is a second or two delay until the regulator responds. This is normal.

How to Test Your Alternator and Voltage Regulator

You can check the functioning of the alternator with a voltmeter. Put the voltmeter across the battery terminals. With engine off, fully charged battery is 12.5-12.7 VDC. With engine on, all accessories off, it should be around 14.6 VDC when engine and alternator are cold. As you start turning on accessories (lights, A/C, A/C blower) voltage will drop. With stock 2G, 75A alternator, voltage will drop below 12.7 VDC. With 3G, 130A alternator, voltage will not drop below 13.0 VDC.

NOTE:  There are 2 reasons for the drop: 1) as the temperature of the alternator increases, the regulated output voltage decreases. This is due to a negative temperature coefficient of the voltage regulator (approx. -10mv/ºC.). If the alternator has a temperature rise of 100ºC (68ºF to 248ºF), the regulated voltage will decrease by 1.0V, 2) as the alternator load increases, the regulated output voltage will decrease.  The 14.6V regulator output is at 0% load.  At 6000rpm at 90% load, the voltage will decrease 0.3V. After the alternator reaches operating temperature (which is hot!) and you put a heavy load on it, you will see a voltage ouput of about 13.0V.  As long as the alternator output voltage is slightly higher than the full charge of the battery (12.5-12.7V), the alternator (not the battery) will be supplying the current to the vehicle, and therefore, you are neither charging nor discharging the battery.

Alternator Basics

An alternator is a 3-phase AC generator with diodes to full wave rectify the AC. The battery acts as a big capacitor to smooth out the AC ripple. The voltage regulator tries to keep the voltage constant with a varying load.

There is a diode pack with 6 diodes. If only one goes bad (bad being a short, but it could also fail open), you will not have a short to ground. Your alternator voltage output will be less than it should be with more AC than the battery or voltage regulator can tolerate.

When performing this upgrade, do not remove any of the wires from the Starter Relay.   You can damage the alternator and blow one of the diodes because the regulator is effectively out of the circuit.  If you blow 2 series diodes, you will melt the alternator charge wire and maybe start a fire. That's why you need to fuse the charge wire and that's why Ford had it fused with a Fuse Link.

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Ford Drawings for 1988

The two diagrams below are excerpted from "Electric and Vacuum Troubleshooting Manual", FPS-12121-88; Copyright © 1987 Ford Motor Company.

3G, 130A Alternator & Fuse - Installed

How to Test for an Unexplained Drained Battery

You have parked your car for a couple days and when you try to start it, the battery is dead.  You have just replaced the battery, so you know that is not the problem.   You think it could be the alternator or the starter, how do you know?

First, you need to test for proper operation of the alternator.  Follow my procedure outlines above.  If the battery is O.K. and the alternator is O.K., you probably have a short somewhere that's causing a current drain.

You need an ammeter connected in series with one of the battery legs. Make sure everything is off, since most ammeters are limited to 10A. You should see a current draw of >1.0A, if you have a problem somewhere. Start pulling fuses to find what circuit is affected.

Many times it is a corroded exterior light bulb/socket.  I've had the underhood light not go off when the hood was closed.  It could also be a bad cigarette lighter. I've had all these happen to me.

Alternator Questions and Answers:

Q1:  If I'm not mistaken, I just plug in the smaller oval connector to the new 130A right?

A1:  Correct.

Q2:  Which wire off the old connector do I splice with the stator wire connector?

A2:  Splice into White/Black wire which is the center one on the oval connector and the end one on the big square connector (which you don't even have to cut off).  Use the crimp on trailer light connectors so you don't have to solder.

Q3:  Do I just follow the other two back until I find where they split, cut it, and splice in my 4 AWG wire?

A3:  No.  Run the new 4AWG wire from the stud on the back of the new 3G, through the new fuse, and then to the battery.  Leave the old Black/Orange wires alone and definitely don't remove anything from the starter relay end.

Q4:  So I splice into BOTH the White/Black wire on the oval plug, and the White/Black wire on the square plug for the stator wire connector?  Or did you mean that they're connected down the line somewhere?

A4:  It's the same wire on both plugs.  It just loops from one plug to the other.  Take a look at the drawing above.

Q5:  I'm moving my battery to the trunk, so can I just run the 4 AWG cable to where the positive battery cable runs to?

A5:  Yes, that's right.  Make sure the battery cable from the starter relay to the plus battery terminal (which is about 15-20 ft long) is at least 2AWG.  The minus battery cable can go to the chassis, but make sure there is another one from the chassis to the engine block.  If the 2 minus cables are short (less than 2 ft), they can be 4AWG if necessary.

Q6:  It's about the two wires that were left over from the square connector.  Do I just cut and tape them off, or do I need to run them to the stud on the alt. too?

A6:  You could do it either way.  I just left the big square connector on, plugged into nothing.  If I ever wanted to put a 2G in (don't know why), I could.

Q7:  What I mean is, do these wires serve any purpose now?

A7:  They serve an important purpose by being connected at the other end (at the starter relay).  The statement "...you can either take the 2-1 10gauge wire out or just tape both ends and get it out of the way..." is incorrect.   Your regulator won't work properly if you disconnect the 10AWG wire at the starter relay.  If you do remove the 10AWG wire at the starter relay, you have also inadvertantly removed the Yellow/White wire from the starter relay.  This wire comes from the d-plug and is required for the regulator is work properly.

Q8:  Why would you run the thick wire from the d-plug all the way to the solenoid when you can just connect it to the post on the alternator, with a fuseable link of course?

A8:  I don't exactly understand what you are saying but you are confusing starter solenoid with starter relay.  You are not running a thick wire from the d-plug to the solenoid or to the post on the alternator.  I was referring to the Black/Orange wire that was already on the starter relay.  If you remove it from the starter relay, you have also removed the Yellow/White wire without realizing it.  The thick wire (4AWG) goes from the alternator stud, through a fuse and to the starter relay.   A 2AWG (or larger) wire goes from the starter relay to the battery in the trunk. You are not doing anything with the starter solenoid.  Look at the drawing above and pay particular attention how Fuse Link E connects to Fuse Link F which connects to the starter relay.  Save the P12 drawing to your computer and zoom in so you can read it better.

Q9:  I'm sorry when I was talking about a thick wire I was just designating the thicker (12gauge?) of the three on the d-plug. That wire runs parallel with the factory 10AWG power lead and splices into it right before the fuse link right before the solenoid.  Since I decided to rewire the whole thing I just spliced that thicker wire (#36 ford schematic) right into the power lead coming off the alternator, this would be the same thing as running all the way to the solenoid just like the factory.   So in essence I have a 1 wire alternator with an extra wire for the indicator bulb in the dash.

A9:  I understand what you did now, but it's not exactly the same.  Ford had a reason for wiring it the way they did.  Here's why:  The #36 wire is a voltage sense wire, that is intended to sense the true voltage at the battery not the alternator's output.  These are not necessarily the same because as the current increases in #38 wire (now the 4AWG), the IR drop in the wire creates a voltage that is less at the starter relay than at the alternator output.  What you've done is sense the voltage at the alternator instead of the battery (or as close to it as you can get).  In your configuration, you will be getting poor voltage regulation at higher current outputs of the alternator.  That's another reason why if you move your battery to the trunk, you want the + lead to be large gauge, because you have increased the distance from the sense to the battery.  Test it by turning all electrical accessories on at the same time and measure the voltage across the battery. It should be no less than 13.2V (12.7V for fully charged battery + .5V). Do this when engine is cold and when engine is hot; should be >13.2V when hot and >14V when cold.

Q10:  But isn't that how single wire alternator works; I've seen 240amp single wires before.

A10:  I'm not sure exactly how they work, but I suspect the voltage regulator has a higher set point and they just allow the regulator to have a wider swing.  Commercial DC power supplies use the same sensing scheme.  They can work without the sense at high current loads, they just don't regulate the output voltage very well.

Q11:  Would the best possible thing be to run #36 all the way to the battery?

A11:  Yes.  However, if you run 0AWG, it's probably not necessary.  I need to do this myself, so I can't verify if effectiveness yet.   It's not a problem with the stock location, because the + battery cable is only about 1 ft long.  I've got about an 6-8 ft run of 2AWG, because my battery is on the passenger side.

Q12:  Right now I have about 5 feet of 1AWG between the alternator and solenoid and about 14 ft of 2AWG between the solenoid and battery.  I was considering using AWG to the battery; would this make any difference?

A12:  I'm sure you mean "relay" not "solenoid".  I would consider 2AWG to be minimal. 1AWG or 0AWG would be best, especially when trying to start the vehicle in cold weather or a weakened battery.   Also, you would not need to run #36 all the way to the battery.

Q13:  I'm still having problems charging even though I've connected everything as you described.  What's wrong?

A13:  It's possible one of the fuse links is blown.  You can't tell by looking at them, but you will generally be able to feel a soft spot somewhere along the link.  Check out the fuse links described in Answer #8 above.

Alternator Connections for Other Years:

On your 84 external voltage regulator, you have the following:
F, S, A, I

Unplug the wiring harness going into the external voltage regulator. Either splice into with your new wire or make a blade connector that will go into the old wiring harness.   You will need to tap into two of those wires:
The F will not be used.
The S will go directly to the I on the 3G. The A will go directly to the A on the 3G. The I will not be used.

Looking at it from the 3G viewpoint:

The BAT goes to the inline fuse.
The stator connector goes to the S connector on the 3G.
The A connector goes to the A wire on the old wiring harness.
The S connector goes to the stator connector on the back of the 3G.
The I connector goes to the S wire on the old wiring harness.

Revised: December 13, 2004 02:40 PM