Alternator and Regulator Wiring

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I've thought about making up color-coded wiring diagrams focused on the alternator and voltage regulator for some time. The question came up again the other day on how and what the different wires were connected to.

So, I decided to do it, one diagram for cars without factory ammeters, one for cars with factory ammeters, and a bonus of a 3G wiring diagram.

If anybody spots any errors, please let me know, so I can correct it.

View attachment 40168

EDIT: updated diagrams 05132018

 
Last edited by a moderator:
I've thought about making up color-coded wiring diagrams focused on the alternator and voltage regulator for some time. The question came up again the other day on how and what the different wires were connected to.

So, I decided to do it, one diagram for cars without factory ammeters, one for cars with factory ammeters, and a bonus of a 3G wiring diagram.

If anybody spots any errors, please let me know, so I can correct it.

View attachment 40168

EDIT: updated diagrams 05132018
Greetings Don!

This is a long one, and I ask you, respectfully, to bear with me. I believe your reading the following will be very useful to you, and many others who (also) learn from your postings...

The alternator wiring schematics you provided in the 7173Mustangs.com Tutorial are very nicely done. Very clear. I do, however, have two areas I would like to put forth for your consideration in making a few adjustments. I have attached an Enhanced version of your schematic pages. The enhancements are the same for all 3 pages. The first is self-evident, where I simply identified the "S" and "I" terminals on the Starter Relay, which "S" and "I" characters are often provided as raised letters on the molded Relay housing. I did take note that like myself, and some (not all) older schematics the Circuit "32" has a "32A" designation indicating something "different" about the otherwise same Circuit with respect to the function of the circuit segments. I found that kind of clarification to be useful.

The other enhancement is one that is lost upon a lot of folks as it was explained incorrectly by so many "experts" for many years. I only became aware of my having followed the "conventional thinking crowd" myself back when I was a young kid just learning about automobile repair. I was taking an Automotive Electrical Systems class, as part of the curriculum required for my A.S. in Automotive Repair Technology. The instructor was a former boxer by the name of Joe Renzi. He was a very likable gentleman who had many decades of electrical experience. When he began to cover the way the Ford Starting system worked he said, "Your book is wrong in one area, and I need all of you to pay close attention to what I about to tell you. You will find many mistaken ideas about auto repair in your lifetime, but this is a big one that will change everything you ever believed about electricity."

He then asked what the cranking voltage of the battery ought to be when testing the Cranking Circuit. I raised my hand and said, "We are looking for 200 - 250 amps on a V-8, with about 10.5 - 11.5 volts, but no less than 9.6 volts." "Close enough," Joe responded. "So, let me ask you this. In your book it says the Starter Relay supplies 12 volts to the Ignition Coil while the engine is cranking. Does everybody see that? Do you understand why?" I raised my hand, again, and said, "I sense a trick question here, but as I understand it the 12 volts is supplied to the coil to make certain the high voltage output of the coil is higher to help start the engine." "Yes," he said, "And that is precisely where the problem is. How do you get 12 volts to the coil while the engine is cranking over when the battery voltage has dropped below 12 volts? The bigger truth is the Starter Relay provides FULL BATTERY VOLTAGE - that much is true. But it is not 12 volts, as 12 volts does not exist during cranking. All you have is 11.5 volts at best for a small engine, and maybe as low at 9.6 volts on a larger engine. Even less with a battery that is not fully charged or worn down due to prolonged cranking."

Wow, he was right. Now it all made perfect sense. The normal running voltage of 10 volts, more or less, sent to the ignition coil is about what cranking voltage is. So, the ignition bypass to get battery voltage to the coil during cranking was nothing more than an attempt to get the voltage normally see when running, not to get 12 volts to the coil for better starting.

Ever since then I have been plagued with the knowledge that the oft quoted "Full 12 Volts" during cranking ignition bypass is entirely wrong. Usually it is something I find where I can't do much about it (a book or magazine). But, where I can share that insight I will, in conjunction with a heartfelt desire to not make anyone feel badly about being essentially hoodwinked for years with this one misunderstanding.

I share this with you for a few reasons. First, clearly you are respected and renowned member of the automotive repair field. Especially when it comes to Mustangs (and Shelbys). Second, with all the knowledge you clearly possess I feel you, of all people, will "get it" when I seek to reveal this tidbit to you. And I feel it is very unlikely you will be upset as you will be able to discern the spirit in which I share this with you. That said, I have enhanced your PDF file by first identifying the "S" and "I" terminals on the Starter Relay part of the schematics. And at the end of the "I" wiring in the schematic, I altered the explanation very slightly to provided more correct info re: what is being sent to the Ignition Coil, and even a brief explanation as to why that is the case.

I offer this in the spirit of one car guy who is always trying to learn more, and shares what he knows freely, to another car guy who has what I feel is a similar outlook on what his role is in our little community of enthusiasts and auto repair professionals. Please feel free to share this enhanced version, or a revision of your own reflecting this new and profound way of thinking, with others as you see fit and appropriate.

I will continue to look for more information from you in the future. It is a shame we live in areas so far apart from each other. I feel if we were residing in the same area we could become quite formidable, in a good way.
 

Attachments

  • Ford Alternator Wiring v2_GMH_Enhanced_20220512.pdf
    2.7 MB · Views: 21
The purpose of the line from starter solenoid to coil is to provide battery voltage, as you correctly state, in lieu of the normal voltage supplied by the ignition switch/1.5 ohm resistor wire circuit used when the starter is not being cranked. In addition to lower voltage while cranking, the resistor wire further lowers voltage to the coil, such that there may not be enough voltage to engage the secondary ignition system with sufficient voltage to fire the spark plugs.

Put simply (but slightly incorrectly), while cranking, the coil gets full battery voltage (as much as can be supplied) vice lower voltage through the normal circuit. Systems without a resistor wire would see the same voltage at the coil through either system while cranking.
 
Greetings Don!

This is a long one, and I ask you, respectfully, to bear with me. I believe your reading the following will be very useful to you, and many others who (also) learn from your postings...

The alternator wiring schematics you provided in the 7173Mustangs.com Tutorial are very nicely done. Very clear. I do, however, have two areas I would like to put forth for your consideration in making a few adjustments. I have attached an Enhanced version of your schematic pages. The enhancements are the same for all 3 pages. The first is self-evident, where I simply identified the "S" and "I" terminals on the Starter Relay, which "S" and "I" characters are often provided as raised letters on the molded Relay housing. I did take note that like myself, and some (not all) older schematics the Circuit "32" has a "32A" designation indicating something "different" about the otherwise same Circuit with respect to the function of the circuit segments. I found that kind of clarification to be useful.

The other enhancement is one that is lost upon a lot of folks as it was explained incorrectly by so many "experts" for many years. I only became aware of my having followed the "conventional thinking crowd" myself back when I was a young kid just learning about automobile repair. I was taking an Automotive Electrical Systems class, as part of the curriculum required for my A.S. in Automotive Repair Technology. The instructor was a former boxer by the name of Joe Renzi. He was a very likable gentleman who had many decades of electrical experience. When he began to cover the way the Ford Starting system worked he said, "Your book is wrong in one area, and I need all of you to pay close attention to what I about to tell you. You will find many mistaken ideas about auto repair in your lifetime, but this is a big one that will change everything you ever believed about electricity."

He then asked what the cranking voltage of the battery ought to be when testing the Cranking Circuit. I raised my hand and said, "We are looking for 200 - 250 amps on a V-8, with about 10.5 - 11.5 volts, but no less than 9.6 volts." "Close enough," Joe responded. "So, let me ask you this. In your book it says the Starter Relay supplies 12 volts to the Ignition Coil while the engine is cranking. Does everybody see that? Do you understand why?" I raised my hand, again, and said, "I sense a trick question here, but as I understand it the 12 volts is supplied to the coil to make certain the high voltage output of the coil is higher to help start the engine." "Yes," he said, "And that is precisely where the problem is. How do you get 12 volts to the coil while the engine is cranking over when the battery voltage has dropped below 12 volts? The bigger truth is the Starter Relay provides FULL BATTERY VOLTAGE - that much is true. But it is not 12 volts, as 12 volts does not exist during cranking. All you have is 11.5 volts at best for a small engine, and maybe as low at 9.6 volts on a larger engine. Even less with a battery that is not fully charged or worn down due to prolonged cranking."

Wow, he was right. Now it all made perfect sense. The normal running voltage of 10 volts, more or less, sent to the ignition coil is about what cranking voltage is. So, the ignition bypass to get battery voltage to the coil during cranking was nothing more than an attempt to get the voltage normally see when running, not to get 12 volts to the coil for better starting.

Ever since then I have been plagued with the knowledge that the oft quoted "Full 12 Volts" during cranking ignition bypass is entirely wrong. Usually it is something I find where I can't do much about it (a book or magazine). But, where I can share that insight I will, in conjunction with a heartfelt desire to not make anyone feel badly about being essentially hoodwinked for years with this one misunderstanding.

I share this with you for a few reasons. First, clearly you are respected and renowned member of the automotive repair field. Especially when it comes to Mustangs (and Shelbys). Second, with all the knowledge you clearly possess I feel you, of all people, will "get it" when I seek to reveal this tidbit to you. And I feel it is very unlikely you will be upset as you will be able to discern the spirit in which I share this with you. That said, I have enhanced your PDF file by first identifying the "S" and "I" terminals on the Starter Relay part of the schematics. And at the end of the "I" wiring in the schematic, I altered the explanation very slightly to provided more correct info re: what is being sent to the Ignition Coil, and even a brief explanation as to why that is the case.

I offer this in the spirit of one car guy who is always trying to learn more, and shares what he knows freely, to another car guy who has what I feel is a similar outlook on what his role is in our little community of enthusiasts and auto repair professionals. Please feel free to share this enhanced version, or a revision of your own reflecting this new and profound way of thinking, with others as you see fit and appropriate.

I will continue to look for more information from you in the future. It is a shame we live in areas so far apart from each other. I feel if we were residing in the same area we could become quite formidable, in a good way.
Yes, you are correct about voltage available while cranking. I usually also call it battery voltage. I must have been trying to save space, or lazy, and just called it 12 volts. Because we cannot edit posts made before the latest server upgrade I will repost a corrected version.
Thank you for bringing this to my attention.
Not only does the battery voltage drop while cranking, but because of the resistor circuit going to the coil from the ignition switch, the voltage to the coil also drops. With 12 volts the coil receives about 6 volts through the resistor circuit. If the available voltage is 10.5 volts the voltage to the coil drops to about 5 volts through the resistor circuit.
 
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The purpose of the line from starter solenoid to coil is to provide battery voltage, as you correctly state, in lieu of the normal voltage supplied by the ignition switch/1.5 ohm resistor wire circuit used when the starter is not being cranked. In addition to lower voltage while cranking, the resistor wire further lowers voltage to the coil, such that there may not be enough voltage to engage the secondary ignition system with sufficient voltage to fire the spark plugs.

Put simply (but slightly incorrectly), while cranking, the coil gets full battery voltage (as much as can be supplied) vice lower voltage through the normal circuit. Systems without a resistor wire would see the same voltage at the coil through either system while cranking.
Yes, I have noticed the slight variance between voltage levels when cranking the engine at different spots I check, to include the even lower voltage coming from the ignition switch's resistor wire during cranking. I only checked for giggles and grins. Your point is well taken, and in the spirit in which it was intended, no doubt. Gawd, all of this old school electrical system stuff can be so much fun. Frustratingly fun, but still fun...
 
Another item that is not well known is why there is a recommendation not to crank the engine for an extended period of time. Doing so causes the full battery voltage to go directly to the coil via a 18 gauge wire. While cranking, there are periods of grounding via the points. Thus, while cranking, that 18 gauge wire is trying to handle ~12V directly to ground and can burn the insulation off during excessive times of cranking. I've actually encountered one instance of that via a customer of mine.
 
Another item that is not well known is why there is a recommendation not to crank the engine for an extended period of time. Doing so causes the full battery voltage to go directly to the coil via a 18 gauge wire. While cranking, there are periods of grounding via the points. Thus, while cranking, that 18 gauge wire is trying to handle ~12V directly to ground and can burn the insulation off during excessive times of cranking. I've actually encountered one instance of that via a customer of mine.
That's very true. You can see what the load differences are in this illustration, with and without a ballast resistor and running or stopped with the points closed. The cranking current will be somewhere between the two,
Coil and Ballast Resistance.jpg
 
OK, my head is going to explode! :)
My question revolves around making upgrades. From what I have read, IF I upgrade the following:
*stock coil for a 0.6 ohm Flame Thrower coil;
*upgrade the voltage regulator to an electronic version;
*upgrade the distributor with a Pertronix electric ignition module;
**do I need to replace the resistor wire from the ignition switch to the coil with regular wire??
1657816591775.png
The reason for this question is due to the car came with an MSD 6AL ignition box - that has failed, so now, short of putting it back stock, I would like to convert to electronic ignition.
Additionally, the motor is stock and really doesn't require the MSD or the extreme cost.

Thanks, Electric Gurus!
 
OK, my head is going to explode! :)
My question revolves around making upgrades. From what I have read, IF I upgrade the following:
*stock coil for a 0.6 ohm Flame Thrower coil;
*upgrade the voltage regulator to an electronic version;
*upgrade the distributor with a Pertronix electric ignition module;
**do I need to replace the resistor wire from the ignition switch to the coil with regular wire??
View attachment 65685
The reason for this question is due to the car came with an MSD 6AL ignition box - that has failed, so now, short of putting it back stock, I would like to convert to electronic ignition.
Additionally, the motor is stock and really doesn't require the MSD or the extreme cost.

Thanks, Electric Gurus!
The easiest I think is to add an ignition relay that is activated by the stock ignition wire.
 
OK, my head is going to explode! :)
My question revolves around making upgrades. From what I have read, IF I upgrade the following:
*stock coil for a 0.6 ohm Flame Thrower coil;
*upgrade the voltage regulator to an electronic version;
*upgrade the distributor with a Pertronix electric ignition module;
**do I need to replace the resistor wire from the ignition switch to the coil with regular wire??
View attachment 65685
The reason for this question is due to the car came with an MSD 6AL ignition box - that has failed, so now, short of putting it back stock, I would like to convert to electronic ignition.
Additionally, the motor is stock and really doesn't require the MSD or the extreme cost.

Thanks, Electric Gurus!
Hey there Carguy47,
Not sure what what you have but on my 73 302 I was able to pickup switched battery that didn’t drop out during crank for my Pertronix from the throttle position solenoid. I pulled back the boot and soldered to the lug, it blends in nicely and after going through the electrical drawings I was satisfied with this solution, definitely look at it closely for your application. I was going to show the page from the wiring diagram manual but I don’t know if that’s ok.
I hope this helps

Bryan
5787E7B1-2E7B-41C0-A027-93C846DF84F9.jpeg558BC43E-2E5D-498E-9972-145C5708D169.jpeg
 
Thanks guys.
The PO replaced the 351C/C6 with a 302/C4 and his wiring/auto skills were not the best.
Fortunately, I think he left all the original wiring laying in the engine bay. (I think)
 

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  • 302.jpg
    302.jpg
    180.8 KB · Views: 2
Hey there Carguy47,
Not sure what what you have but on my 73 302 I was able to pickup switched battery that didn’t drop out during crank for my Pertronix from the throttle position solenoid. I pulled back the boot and soldered to the lug, it blends in nicely and after going through the electrical drawings I was satisfied with this solution, definitely look at it closely for your application. I was going to show the page from the wiring diagram manual but I don’t know if that’s ok.
I hope this helps

Bryan
View attachment 65696View attachment 65697
Of I recall correctly, the Throttle Position Solenoid (TPS), using Circuit 640 for its power source, began to appear in 1971, and is included in 1972 & 1973. I am not certain if all carburetors in 1971, 1972 & 1973 used a TPS or not, but the wiring is there in any event. I have found it to be an excellent place to tap into for full battery switched power. But, it gets its power through Fuse #4, a 14 amp fuse. Thus I do not use it to power high current demand systems. It is fine for powering the trigger power circuit for aftermarket relays (horn, headlight, electric fan).

An alternative place I have tapped into full battery switched current is the Windshield Wiper Motor circuit # 63, the Red wire that provides switched power to the Windshield Wiper Motor. It is fed through the Windshield Wiper Motor Switch, which in turn is fed via Circuit #296 which is protected with just a 14 amp fuse (Fuse 1). Thus I do not use it to power high current demand systems. It is fine for powering the trigger power circuit for aftermarket relays (horn, headlight, electric fan).
 
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Yes, circuit #640 is under the hood on all '71s. From what I can tell, the only '71 that used to throttle position solenoid was the 6 cylinder with an automatic transmission. For the rest I believe that it terminates at a white connector.
 
The easiest I think is to add an ignition relay that is activated by the stock ignition wire.
That is not a bad way to go. But it would be simpler to use either the Throttle Position Solenoid or Wiper Motor switched power circuits from under the hood area to provide full battery voltage to a full voltage ignition coil. But, frankly, for a stock engine build, or even a moderate street/strip engine that will not be hitting higher RPMs very often (if ever), I would likely opt to keep a stock point/condenser ignition system. Simple and plenty adequate for street use. And, for folks who understand how the old school systems work, it is easy to diagnose in the event of a problem. The biggest problem I have found with the old school point/condenser systems is found when the distributor cam lobes for the ignition point unit is not very lightly lubed, and the rubbing block on the points assembly wears down very quickly. I have also seen one case where too much lubricant was used on the point cam lobes let grease droplets accumulate on the points' surface, which created an electrical impediment as the arcing burned the grease and made a glob of burned grease act like an insulator.

That said, we do have a complete MSD ignition system, including an MSD distributor, on out 73 Mustang Mach 1 which has a transplanted 351W (not C) street/strip built engine. I swapped the MSD 6AA ignition module out with an MSD 6AL Auto Limiter module, just because, and now have the 6A unit on hand as a spare in case the 6AL fails as some point. The MSD system does work well, but had the engine come to us with the original ignition system I would have left it in place. It is rare we hit RPMs at the level where the electronic ignition system(s) do any real good beyond the stock systems.
 
In Pertronix's quest to make their systems easy to install, they make them more complicated. I prefer this setup:

B. Alternative Installation: The Ignitor II can also be installed in applications retaining the ballast resistor or resistance wire.
• Attach the Ignitor II black wire to the negative coil terminal. Attach the Ignitor II red wire to the ignition side of resistance, or any 12 volt ignition power source
.

Connect the Ignitor red power wire to the Throttle Position Solenoid feed wire, it's the red w/yellow hash with the single female bullet at the firewall - RED arrow below. It has full battery voltage in both START and RUN, so it's perfect for this application.

71_TPS_WIRING.JPG
 
In Pertronix's quest to make their systems easy to install, they make them more complicated. I prefer this setup:

B. Alternative Installation: The Ignitor II can also be installed in applications retaining the ballast resistor or resistance wire.
• Attach the Ignitor II black wire to the negative coil terminal. Attach the Ignitor II red wire to the ignition side of resistance, or any 12 volt ignition power source
.

Connect the Ignitor red power wire to the Throttle Position Solenoid feed wire, it's the red w/yellow hash with the single female bullet at the firewall - RED arrow below. It has full battery voltage in both START and RUN, so it's perfect for this application.

View attachment 65729
I put together a short video on where the Throttle Position Solenoid and Red-Yellow Hash tracer wire (Circuit #640) is located at:

 
Thank you all for the great and informative suggestions. Going to give it a go sometime later today.
(as long as the 110 degrees doesn't bake me first, it's 10am and already 100)
 
Alright guys, I found the wiring harness connector and I am ready to complete my conversion. Now I have 2 final questions:
First, does someone make a replacement male connector to fit the harness? Or, do I just cut and install insulated spade connectors.
Second, since the PO installed an aftermarket carb, can I pull power from this connection to also feed the electric choke? Or, will it draw to much and negatively impact the coil operation?

Thanks, Bill
 
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