1973 Mustang Alternator Applications

[Steve73QMach1]

The alternators used in 1973 Mustangs have always been a point of confusion for me. The Ford schematics and shop manuals show 42 amp, 55 amp, 61 amp, and 70 amp alternators as applicable parts for a 1973 Mustang. The 70 amp alternator is unique in that it has a different configuration for the wire harness. One would think that a low optioned six cylinder car might have received the 42 amp version and that a highly optioned V8 would get the 70 amp model. I have a Mach 1 with a 70 amp alternator (has power windows and rear window defrost). Another member of this forum, jeff8877, has a highly optioned Mach 1 and it appears that his came with a 55 amp alternator. There are people out there that say the 70 amp alternator was not used on the Mustang at all. There are a few members on this forum that have 70 amp alternators that I know of. Unfortunately, the Marti report or the Emminger invoice did not mention anything about alternator choices. I have the original order form for my 4 speed car and it makes no mention of a specific alternator type. That leads me to believe that the alternator choice was made based on the options that the car had installed at the factory. I presume that the vast majority of the 1973 Mustangs came with the 55 amp alternator. I am interested in hearing from any forum members on this topic - what alternator do you have with which options? If you have a 70 amp alternator, do you also have rear window defrost and/or power windows? Do you have a 55 amp alternator with power windows or rear window defrost? Does anyone have a 42 amp or a 61 amp alternator? I will attempt to digest all of the inputs and try to understand what rationale was used during assembly of these cars. If you know your build date, please supply that as well. In addition, if you have your build sheet, check row D, character positions 16 and 17 for the alternator code used on your car. Hopefully with enough inputs we can figure out what parameters were in place to determine alternator size for these cars.

 

[jbojo]

The alternators used in 1973 Mustangs have always been a point of confusion for me The Ford schematics and shop manuals show 42 amp, 55 amp, 61 amp, and 70 amp alternators as applicable parts for a 1973 Mustang. The 70 amp alternator is unique in that it has a different configuration for the wire harness. One would think that a low optioned six cylinder car might have received the 42 amp version and that a highly optioned V8 would get the 70 amp model. I have a Mach 1 with a 70 amp alternator (has power windows and rear window defrost). Another member of this forum, jeff8877, has a highly optioned Mach 1 and it appears that his came with a 55 amp alternator. There are people out there that say the 70 amp alternator was not used on the Mustang at all. There are a few members on this forum that have 70 amp alternators that I know of. Unfortunately, the Marti report or the Emminger invoice did not mention anything about alternator choices. I have the original order form for my 4 speed car and it makes no mention of a specific alternator type. That leads me to believe that the alternator choice was made based on the options that the car had installed at the factory. I presume that the vast majority of the 1973 Mustangs came with the 55 amp alternator. I am interested in hearing from any forum members on this topic - what alternator do you have with which options? If you have a 70 amp alternator, do you also have rear window defrost and/or power windows? Do you have a 55 amp alternator with power windows or rear window defrost? Does anyone have a 42 amp or a 61 amp alternator? I will attempt to digest all of the inputs and try to understand what rationale was used during assembly of these cars. If you know your build date, please supply that as well. In addition, if you have your build sheet, check row D, character positions 16 and 17 for the alternator code used on your car. Hopefully with enough inputs we can figure out what parameters were in place to determine alternator size for these cars.

Steve,

So you have a GPD alternator with side terminals? I know mine has the rear terminals so I'll have to dig it out to find out the Amps. The alternators have color codes for the rear connection ones.

Orange = 42 A

Red = 55A

Green =61A

My build sheet as a code of 5B for my car.

-jbojo

 

[jb73Mach]

I posted on the other thread before I saw this one. My '73 has code 7A on the build sheet. The alternator does not look original so I do not think anything on the case will be of much use. With the rear defrost, I should have had a higher amp alternator.

 

[73mach1]

Mine is a q code with no a/c , no rear window defrost,and no power windows. I can't read my build sheet, but I have a red wire going to my alt so I guess it's a 55 amp.

 

[jeff8877]

jbojo...

The color codes you mentioned...are those paint marks on back of alt or different wire colors or different color insulators on alt?

The alternators have color codes for the rear connection ones.

Orange = 42 A

Red = 55A

Green =61A

Jeff

 

[jbojo]

jbojo...

The color codes you mentioned...are those paint marks on back of alt or different wire colors or different color insulators on alt?

The alternators have color codes for the rear connection ones.

Orange = 42 A

Red = 55A

Green =61A

Jeff

Jeff not sure, I pulled the color codes from the service manual for 73. I'll go out and dig up my alternator and see if it has color codes on it. I do not believe that those are the wire colors.

-jbojo

 

[jeff8877]

Steve,

73 Mach Q code

Build Date...6/12/73

High draw options...A/C, power windows, rear defrost

Build sheet...not legible

Alternator harness...rear mount type

Alternator...original unknown

Volt Reg Part #...original unknown

Trans...C6 auto

Jeff

 

[Steve73QMach1]

jbojo...

The color codes you mentioned...are those paint marks on back of alt or different wire colors or different color insulators on alt?

The alternators have color codes for the rear connection ones.

Orange = 42 A

Red = 55A

Green =61A

Jeff

Jeff not sure, I pulled the color codes from the service manual for 73. I'll go out and dig up my alternator and see if it has color codes on it. I do not believe that those are the wire colors.

-jbojo

Jeff,

According to some documentation I found, those colors were inked on the back of the alternator for ID purposes. the 70 amp alternators received no color code. The amp rating of the alternator was also impression stamped on the case. jbojo is correct - they are not the wire colors.

The alternators used in 1973 Mustangs have always been a point of confusion for me The Ford schematics and shop manuals show 42 amp, 55 amp, 61 amp, and 70 amp alternators as applicable parts for a 1973 Mustang. The 70 amp alternator is unique in that it has a different configuration for the wire harness. One would think that a low optioned six cylinder car might have received the 42 amp version and that a highly optioned V8 would get the 70 amp model. I have a Mach 1 with a 70 amp alternator (has power windows and rear window defrost). Another member of this forum, jeff8877, has a highly optioned Mach 1 and it appears that his came with a 55 amp alternator. There are people out there that say the 70 amp alternator was not used on the Mustang at all. There are a few members on this forum that have 70 amp alternators that I know of. Unfortunately, the Marti report or the Emminger invoice did not mention anything about alternator choices. I have the original order form for my 4 speed car and it makes no mention of a specific alternator type. That leads me to believe that the alternator choice was made based on the options that the car had installed at the factory. I presume that the vast majority of the 1973 Mustangs came with the 55 amp alternator. I am interested in hearing from any forum members on this topic - what alternator do you have with which options? If you have a 70 amp alternator, do you also have rear window defrost and/or power windows? Do you have a 55 amp alternator with power windows or rear window defrost? Does anyone have a 42 amp or a 61 amp alternator? I will attempt to digest all of the inputs and try to understand what rationale was used during assembly of these cars. If you know your build date, please supply that as well. In addition, if you have your build sheet, check row D, character positions 16 and 17 for the alternator code used on your car. Hopefully with enough inputs we can figure out what parameters were in place to determine alternator size for these cars.

Steve,

So you have a GPD alternator with side terminals? I know mine has the rear terminals so I'll have to dig it out to find out the Amps. The alternators have color codes for the rear connection ones.

Orange = 42 A

Red = 55A

Green =61A

My build sheet as a code of 5B for my car.

-jbojo

Yes - I have the side terminal GPD 70 amp alternator described in Part 31-12 of the 1973 Ford Shop manual. It is interesting that the amp rating on all of the alternators except 70A is at 15V and 2900 RPM. The 70 amp alternator is 15V and 5000 RPM. Maybe the transmission type is also a player here. My car is a 4 speed.

 

[73mach1]

Sorry, I thought it was wire colors, mine has been replaced with a motorcraft but no part numbers that i can find.

 

[jb73Mach]

Steve,

After a quick look, I do have the side pole alternator and the wiring has not been messed with to the best of my knowledge - so probably a 70 amp according to the shop manual. Add that to the 7A on the build sheet.

 

[Steve73QMach1]

Steve,

After a quick look, I do have the side pole alternator and the wiring has not been messed with to the best of my knowledge - so probably a 70 amp according to the shop manual. Add that to the 7A on the build sheet.

Ok John - great info. That makes sense with your rear window defrost option. I hope I can find the build sheets on my cars. I am going to record 7A as the build sheet code for the 70 amp alternator for now. Hopefully we can get some additional confirmation on that code.


For the sake of completeness, I have included some photos of the top of my 70 amp side terminal alternator. This is on a 53,000 mile car and the original owner told me that it had not been changed.

 

[jb73Mach]

Steve,

I have found build sheets in both of my Mustangs over the years. They were under the carpet on the passenger side in both cases. They were in very bad shape but for the current one, still readable for the most part (with bright lights, younger eyes than mine, etc. etc.). I have it stored in an acid free plastic sleeve to hopefully stave off any further deterioration.

 

[Steve73QMach1]

I did a little research and found the following information regarding alternators used in the 1973 Mustangs:

42 Amp - Orange ink stamp, cut in speed 400 RPM (engine speed), 630 watts, rating at 15 volts at 2900 RPM (engine speed), 6 diodes, rear terminal.

55 Amp - Red ink stamp, cut in speed 400 RPM (engine speed), 825 watts, rating at 15 volts at 2900 RPM (engine speed), 6 diodes, rear terminal.

61 Amp - Green ink stamp, cut in speed 400 RPM (engine speed), 915 watts, rating at 15 volts at 2900 RPM (engine speed), 8 diodes (6 plus two boosters), rear terminal.

70 Amp - no color ink stamp, cut in speed 725 RPM (alternator speed), 1050 watts, rating at 15 volts at 5000 RPM (alternator speed), 6 diodes, side terminal.

All alternator choices appear to utilize the same regulator. It is interesting that only the 70 amp alternator is rated in terms of alternator speed as opposed to engine speed.

 

[jeff8877]

Good info Steve,

I find it interesting that the highest rated OEM voltage regulator (D3TF-10316-AA) that I can find for 73's is only rated at 55 amps. Does this just not matter when using a 70 amp alternator system?

Jeff

 

[Steve73QMach1]

Jeff,

The electro-mechanical voltage regulator used in the Mustangs automatically adjusts the field current in the alternator (via the orange/light blue wire to the alternator field terminal) to maintain the alternator output voltage to around 15 volts to charge the battery properly. All four of the Mustang alternator choices have a field current rating of 2.9 amps at 12 volts - regardless of the alternator current output capability. That's why all of the voltage regulators are the same despite the alternator output rating. The regulator doesn't regulate the current output of the alternator as the alternator is self current limiting. If the replacement voltage regulators on the market don't include anything other than applicability to 55 amp alternators, I believe it is simply an error of omission. A regulator that works for the 55 amp alternator will also work with the 70 amp or the 61 or 42 amp alternators.

 

[jbojo]

Looked at my alternator and it is a 55A one. Build sheet has 5B for the code. The car does not have PW or rear window defroster, only AC, PS and PB. Build date 6/28/73.

-jbojo

 

[73StangCoupe]

Gents,

I don't have my build sheet, but looks like I have a 70A.

My car is a 73 Q code Grande coupe, 4 speed, A/C, power windows, rear debugger.

I snapped a picture...great info all. Thanks, I learn something new about my car almost everyday.

Sent from my SCH-I535 using Tapatalk

 

[jeff8877]

73stangCoupe,

Your alternator has a D7 part number which is from a 1977. Since many of the alternators have been replaced the only way to tell if it originally came from the factory with a 70 amp system is to look at the harness. The 70 amp system had a plug on top of the alternator whereas the 42/55/61 amp systems had a rear electrical attachment without a plug.

Can you look at yours and let us know which type it has...Steve posted a pic of the 70 amp plug type.

Jeff

Gents,

I don't have my build sheet, but looks like I have a 70A.

My car is a 73 Q code Grande coupe, 4 speed, A/C, power windows, rear debugger.

I snapped a picture...great info all. Thanks, I learn something new about my car almost everyday.

Sent from my SCH-I535 using Tapatalk

 

[73StangCoupe]

73stangCoupe,

Your alternator has a D7 part number which is from a 1977. Since many of the alternators have been replaced the only way to tell if it originally came from the factory with a 70 amp system is to look at the harness. The 70 amp system had a plug on top of the alternator whereas the 42/55/61 amp systems had a rear electrical attachment without a plug.

Can you look at yours and let us know which type it has...Steve posted a pic of the 70 amp plug type.

Jeff

Gents,

I don't have my build sheet, but looks like I have a 70A.

My car is a 73 Q code Grande coupe, 4 speed, A/C, power windows, rear debugger.

I snapped a picture...great info all. Thanks, I learn something new about my car almost everyday.

Sent from my SCH-I535 using Tapatalk

Hey Jeff... thanks for the info. As I said I'm always learning.

Let me know if this works...

Sent from my SCH-I535 using Tapatalk