Alternator drawing amps with engine off - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 5 Old 05-05-2012, 10:37 PM Thread Starter
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Alternator drawing amps with engine off

OK-
I recently re-clocked my 3g alt-
I have never started the engine yet, but had the key on to work on some other things. My hand touched the alternator pulley and noticed it was warm. Busted out the laser thermometer and sure enough it was 95* (65* day outside). Turned the key off for 10-15 mins, the pulley was room temp. I unplugged the alternator 3 wire plug, stator wire and sensing wire (batt in trunk sensing wire goes to charge pin). I installed a amp meter on the charge wire to battery and had zero amps with the key on or off. This tells me there is no amp draw from the battery. I then plugged the 3 wire connector and stator wire back in. Tested for amp draw on charge wire to battery with key on and off, again had zero amp draw from battery. As soon as i connected the sensing wire to the charge pin it pulled 5 amp with the key on and 0 with the engine off. Took the alternator to the parts store and it worked fine, also looked for charge wires to rectifier bridge and none of them are contacting the case.

Anyone see an alternator act like this? Thinking i f'd this thing up re-clocking it...


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post #2 of 5 Old 05-06-2012, 12:54 AM
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if the alternator is warm or very warm if not considered hot to the touch the alternator is bad . The guy at the part store did not test it correctly .


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post #3 of 5 Old 05-06-2012, 01:15 PM Thread Starter
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check this thread out, interesting.

https://forums.corral.net/forums/5-0-...ngine-off.html

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post #4 of 5 Old 05-06-2012, 04:05 PM
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It might help to mention the model year and engine of the car in question. There are differences in how the charging circuits are wired between V6 and V8. As well as other differences over the years.

As others have said, the alternator does draw some power as long as the key is on. The battery is used to power the alternator's field coil.

The important thing is for the power draw to be zero with the key off.

If the alternator is drawing current with the key OFF, could the "A" and "I" terminals be reversed? This would have the effect of turning on the alternator all of the time for a late model Mustang 96+

Last edited by wmburns; 05-06-2012 at 04:14 PM.
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post #5 of 5 Old 05-06-2012, 04:12 PM Thread Starter
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opps sorry

91 with a 3g alt -351w
battery in trunk

yellow "sensing wire" connected to charging pin on back of alt
green wire to oem ford green wire-12v+ when key on
white wire goes to stator

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Last edited by dart408; 05-06-2012 at 04:15 PM.
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