Alternator amp draw - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 14 Old 09-01-2018, 10:28 AM Thread Starter
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Alternator amp draw

Should the alternator draw current with the engine off, key in run? When I unplug the connector on the driver's side with the light green/red wire the current being drawn with drop 4 amps.

I'm trying to figure out why my battery is being drained too the point of being unable to turn the engine over in less than 30 minutes. The battery is less than two years old and I've had it checked by two different shops. This is in a 89' lx 5.0. The alternator is a stock reman from 2013.


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post #2 of 14 Old 09-01-2018, 12:09 PM
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what connector on driver side?

if the alt is drawing current, is it getting hot, is it trying to turn the engine over?

where are you measuring 4 amps with key in run?

sounds like a stereo draw


89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #3 of 14 Old 09-01-2018, 02:00 PM Thread Starter
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Quote:
Originally Posted by indy2000 View Post
what connector on driver side?

It's one of the connectors that connects the body harness to the harness coming out of the drivers side firewall. From the firewall harness it's a round 3 pin with black/yellow, blue, geen/red. From the body harness there's only one of the three wires that continues through, the green red.

if the alt is drawing current, is it getting hot, is it trying to turn the engine over?

The alternator does not get hot or warm. Also doesn't try to turn the engine over.

where are you measuring 4 amps with key in run?

Im disconnecting the battery negative and putting the meter leads inline between the negative post and cable.


sounds like a stereo draw

There is no stereo in the car. I only discovered this after installing a megasquirt. I'll leave the ignition in run while making adjustments instead of working offline.

Questions answered above in the quote.I've been using these two diagrams,
http://www.modularfoxmustangs.com/pdf/Charging.pdf
http://www.modularfoxmustangs.com/pdf/Body23.pdf

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post #4 of 14 Old 09-01-2018, 02:10 PM
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the body harness comes out of the driver side, so have no idea what you are referring to there

the alt cannot be drawing current unless its turning and doing work, otherewise it would be hot

your current draw is somewhere else

having a clamp meter would be easiest to find what is drawing

what you can do now, is pull fuses and see where it goes away

4 amp? you sure not 4 milliamp?

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #5 of 14 Old 09-01-2018, 02:48 PM Thread Starter
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Quote:
Originally Posted by indy2000 View Post
the body harness comes out of the driver side, so have no idea what you are referring to there

the alt cannot be drawing current unless its turning and doing work, otherewise it would be hot

your current draw is somewhere else

having a clamp meter would be easiest to find what is drawing

what you can do now, is pull fuses and see where it goes away

4 amp? you sure not 4 milliamp?
The harness i'm referring too looks like it carries the wiring for the headlights/corner markers and alternator around the front of the car.

I've pulled all fuses in the main from the fuse panel with very little change. I'm am sure it is a 4 amp, not milliamp. It will drop the just the same if i pull the 3 pin connector from the alternator directly. The plug at the alternator and plug on the drivers side are both have the green/red wire,There's continuity between the two points.

The only thing that has led to the drop is either disconnecting the plug on the drivers side or from the alternator. The red/green is hot in run and goes to the regulator.

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post #6 of 14 Old 09-01-2018, 04:03 PM
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put your meter in line with alt, and verify for sure

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #7 of 14 Old 09-01-2018, 05:40 PM Thread Starter
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With the leads inline at the alternator with igniton in run I get 3.6-3.8 amps on the yellow/ white wire that runs back to the starter solenoid. The light green/red that goes back to the charge light/ igniton is .2 amps.

I just had the alternator tested which they said it tested the regulator and diodes. It passed on their tester.

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post #8 of 14 Old 09-01-2018, 08:16 PM
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What yellow wire?
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post #9 of 14 Old 09-01-2018, 08:23 PM Thread Starter
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The 3 wire plug on the regulator has a light green/ red that's 12v in run, white/ black that just loops over to the other plug, and a yellow/ white that runs back to the start solenoid and is always hot.

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post #10 of 14 Old 09-01-2018, 10:31 PM
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oh okay

looks like the reg is faulty


89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #11 of 14 Old 09-01-2018, 11:36 PM Thread Starter
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Even though the parts store said everything tested good I was still unsure and had been contemplating replacing the regulator.

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post #12 of 14 Old 09-02-2018, 02:16 AM
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when the store tests it, does it test for a amp draw?

or does it test for voltage and amperage output?

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #13 of 14 Old 09-02-2018, 02:39 AM Thread Starter
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I don't know. I did ask what exactly was tested and was told voltage, amperage output, and diodes. I didn't think to ask how it checked the diodes. I'll call them tomorrow and see if they can answer if their machine tests for a draw.

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post #14 of 14 Old 10-13-2018, 05:59 PM
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Just wondering. Are we positive that the correct alternator for the application has been used? There are several Ford alternator applications that use one of the wires to "turn on" the alternator. If such an alternator is used in a Mustang application that is sending an "always on" power then the regulator will be on all the time. Likely the alternator will test OK at the auto parts stores because its assumed the alternator is wired and controlled correctly.

Here's some more information should you wish to rebuild your alternator yourself or want more testing information.

Howto perform charging system voltage drop test
https://www.stangnet.com/mustang-for...-drop-test.56/

In the same vein, we are positive there's no power on LG/R wire with the key in the off position.

If the wiring tests OK and it's the correct alternator for this application I have to agree that the regulator is bad.
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