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what amperage is my alternator
alternator amperage
- Thread starter dfuller
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71-73 cars were equipped with alternators of 38, 42, 55 and 61 amps. Which yours was equipped with depended on the options it was built with.
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73s also had a 70 amp with certain options. See chart below.
![IMG_1502[1].JPG](https://cdn.imagearchive.com/7173mustangs/data/attachments/70/70946-0d4ec90e6f9ddc39eaff9889fafe2119.jpg "IMG_1502[1].JPG")
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The 1973 alternators were marked with a colored brush-on paint stripe. And on the larger mounting ear the original amperage rating was actually stamped into that mounting part of the alternator housing. Below (end of my response) is the color chart for 1973 alternators. This may differ for older or newer alternators. And, after all these years it is very likely the alternator has been replaced with a rebuilt or new alternator. If rebuilt it is also possible the rotor and/or stator windings were replaced with a part using a higher or lower count of windings, so despite what the color or stamped capacity is, you may have something different.
The most accurate way to see what your alternator is putting out is to use an ammeter with an inductive clamp, set it for DC amperage (make sure your range can go to at least 80 amps), Zero the ammeter when it has no current flowing through it. Then with the Ignition Key in the Run position place the inductive clamp over the battery's negative cable to see how many amps are being drawn from the ignition and other "Key On" switch position equipment. Then turn the Ignition Key off. Using a jumper wire connect the battery's positive terminal to the alternator Field Wire (Orange with a Blue Stripe).
Be very careful to not let the jumper wire or its connectors touch ground anywhere or said wire and connectors will go up in smoke very quickly. Then start the engine and have someone hold the RPM at 2,000 - 2,500 RPM. While the engine is running at 2,000 - 2,500 RPM place the ammeter inductive clamp around the alternator's output cable and see how many amps are flowing. Return the engine to its normal idle speed and turn off the engine. Then remove the alternator field circuit jumper wire. If you add the amps produced at its output cable to the amps being drawn when the engine was off and the Ignition Key was on, you will have a good read on what it can put out.
Do not run the engine too long with the field circuit jumper in place, as it could end up overcharging the battery, needlessly. One of the larger pieces of test equipment I have is a Sun VAT-40 that is designed to test cranking, charging, and battery systems. It has a wire used to either push battery voltage into a field circuit, or ground the field circuit, depending on the type of charging system design is being used for a car. It actually has a 3 position "momentary" toggle switch where I can move the switch's toggle to the appropriate position (sending battery voltage to the field circuit the older Ford alternators), get my amperage output reading, then release the momentary switch's toggle to its center position where nothing will flow through the test wire.
As an alternative, you can remove the alternator and take it to a parts store with an alternator tester and have them check the amperage output. In our case we have a starter & alternator rebuilding facility that also has a few off-vehicle testers. But, removing the alternator for just that alone is a relative PITA (in my opinion).
Here are the 1973 color codes for different amperage levels, although like I said, it may no longer be accurate due to the alternator having been rebuilt using higher (or lower) output components (from a posting by forum member Steve73QMach1 in April, 2011):
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.
Following is a link to a YouTube video we did showing how I diagnosed a No Output condition of an alternator for our 73 Mach 1. It is not a typical diagnostic test that I ran, as it turns out I had a very specific kind of problem where doing a general diagnostic routine diagnostic series of tests was deemed not necessary. But,it has an interesting twist if nothing else.
https://www.youtube.com/watch?v=-ur-4TSZoRU
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.
If you would like me to do a video on this let me know and Lynda and I will gladly show what I describe above, using inexpensive equipment, like the DVOM/Ammeter in this link:
https://www.amazon.com/gp/product/B07Z398YWF/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
or
https://www.amazon.com/gp/product/B08MX3PTBW/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
or
https://www.amazon.com/KAIWEETS-Temperature-Capacitance-Resistance-Continuity-dp-B08CX6VHWV/dp/B08CX6VHWV/ref=dp_ob_title_def
The most accurate way to see what your alternator is putting out is to use an ammeter with an inductive clamp, set it for DC amperage (make sure your range can go to at least 80 amps), Zero the ammeter when it has no current flowing through it. Then with the Ignition Key in the Run position place the inductive clamp over the battery's negative cable to see how many amps are being drawn from the ignition and other "Key On" switch position equipment. Then turn the Ignition Key off. Using a jumper wire connect the battery's positive terminal to the alternator Field Wire (Orange with a Blue Stripe).
Be very careful to not let the jumper wire or its connectors touch ground anywhere or said wire and connectors will go up in smoke very quickly. Then start the engine and have someone hold the RPM at 2,000 - 2,500 RPM. While the engine is running at 2,000 - 2,500 RPM place the ammeter inductive clamp around the alternator's output cable and see how many amps are flowing. Return the engine to its normal idle speed and turn off the engine. Then remove the alternator field circuit jumper wire. If you add the amps produced at its output cable to the amps being drawn when the engine was off and the Ignition Key was on, you will have a good read on what it can put out.
Do not run the engine too long with the field circuit jumper in place, as it could end up overcharging the battery, needlessly. One of the larger pieces of test equipment I have is a Sun VAT-40 that is designed to test cranking, charging, and battery systems. It has a wire used to either push battery voltage into a field circuit, or ground the field circuit, depending on the type of charging system design is being used for a car. It actually has a 3 position "momentary" toggle switch where I can move the switch's toggle to the appropriate position (sending battery voltage to the field circuit the older Ford alternators), get my amperage output reading, then release the momentary switch's toggle to its center position where nothing will flow through the test wire.
As an alternative, you can remove the alternator and take it to a parts store with an alternator tester and have them check the amperage output. In our case we have a starter & alternator rebuilding facility that also has a few off-vehicle testers. But, removing the alternator for just that alone is a relative PITA (in my opinion).
Here are the 1973 color codes for different amperage levels, although like I said, it may no longer be accurate due to the alternator having been rebuilt using higher (or lower) output components (from a posting by forum member Steve73QMach1 in April, 2011):
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.
Following is a link to a YouTube video we did showing how I diagnosed a No Output condition of an alternator for our 73 Mach 1. It is not a typical diagnostic test that I ran, as it turns out I had a very specific kind of problem where doing a general diagnostic routine diagnostic series of tests was deemed not necessary. But,it has an interesting twist if nothing else.
https://www.youtube.com/watch?v=-ur-4TSZoRU
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.
If you would like me to do a video on this let me know and Lynda and I will gladly show what I describe above, using inexpensive equipment, like the DVOM/Ammeter in this link:
https://www.amazon.com/gp/product/B07Z398YWF/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
or
https://www.amazon.com/gp/product/B08MX3PTBW/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
or
https://www.amazon.com/KAIWEETS-Temperature-Capacitance-Resistance-Continuity-dp-B08CX6VHWV/dp/B08CX6VHWV/ref=dp_ob_title_def
I believe the 70a alternators also had plug in connector in the wiring harness. Other alternators did not.
