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Parasitic draw on fuse 11 in power distribution box

1997 - 2003 F-150

Parasitic draw on fuse 11 in power distribution box

 
  #1  
Old 03-17-2019, 01:30 PM
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Join Date: Mar 2019
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Parasitic draw on fuse 11 in power distribution box


Sorry for the length but I think it all matters. I have a 2002 Ford F-150 that has had a parasitic drain for about two years. It all started when my alternator went out on my way home from work. The truck started running rough and the gauges started jumping all over the place and the truck finally died. I changed the alternator out and then the battery a week later. I began getting an intermittent drain at this point so I went and exchanged the alternator for a new one. The intermittent drain has continued ever since. This drain will drain the battery in an hour when it happens. It may go a month with no issues and then it will be dead every time I get in it for the next month. I can go to the store and in an hour or so come back and it will be dead. The testing I have done recently includes a diode test, voltage drop, checked battery not under load and under load, and a parasitic draw test. All the test check out except the parasitic draw test. I did this test today. This is where it got wired. Initially I had about 440 milliamperes draw. After 8 minutes in the draw went up to 850 milliamperes and after fifteen minutes it went down to 640 milliamperes. At this point the battery voltage had dropped to 11.8 volts so I started doing a voltage drop test on all the fuses and found that fuse 11 in the power distribution box was drawing a good bit of current. I pulled the fuse and the draw dropped to 50 milliamperes. After 37 minutes the draw dropped to 10 milliamperes. I reinstalled the 11 fuse and the draw did not come back. I know the fuse has to do with the alternator field so I would suspect a bad diode but the test checks out when I do it. I canít make any sense of it. Thanks for your help.


 
  #2  
Old 03-17-2019, 03:04 PM
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Join Date: Jul 2004
Location: Easton, Pa.
Posts: 5,880
You need to begin all over due to info over-load.
First, a one hour discharge to a no crank condition is a pretty BIG discharge current wise from a fully charged battery. If the battery was not fully charged, then the discharge time is much shorter. Has to be a reason why.
On an intermittent condition, your checks can miss the cause.
Here is how I would go about it.
A. Fully charge the battery to begin.
B. Remove the heavy charge lead from the alternator. Retouch to the terminal and see if there is a spark when touching.
If yes the Alternator is faulty. Do this any other time the fault occurs. Also on an over night failure, feel the Alternator case for being warm. If yes, the Alternator is faulty when the engine is cool..
C. 600 milliamps is only 6 tenth of 1 amp, not a very heavy draw..
Depends on if the hood is open and light is on, Gem function has not timed out etc.
D. Check charge performance with a voltmeter at the battery.
Start motor, check voltage. Should be elevated toward 15 volts then come down as the battery regains charge and settle at about 14.1 +/- a tenth or so depending on system load.
Don't fall back on any parts changed in the past to be good. They may not be.

Good luck.
 
  #3  
Old 03-17-2019, 03:26 PM
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Join Date: Mar 2019
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Bluegrass

Thanks for your response.
I have checked the battery and yes when I started it was at full charge. While engine is running Iím getting 14.3 volts. Here is another weird thing that this alternator is doing. If I put a full load on the battery ( all thing running) it goes up to 14.5 volts. Should go down. Forgot to mention that earlier.
Just to be clear, when I remove the wire attached to to B+ post and reattach it, shouldnít it spark when reattached since it is connected to to battery?
 
  #4  
Old 03-17-2019, 04:14 PM
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Join Date: Jul 2004
Location: Easton, Pa.
Posts: 5,880
Voltage going up is normal.
The Alternator is suppling the system according to load, not the battery.
The regulator detects the load and raises the Alternator output to compensate.
You don't want the voltage to go lower.
If removing the charge lead (with the engine off) and it sparks, the alternator is faulty.
The sparking will be an indication the Alternator is passing battery power to ground discharging the battery.
You don't want this to happen with a non rotating Alternator.
If you have this condition, the Alternator will still charge the battery while running but discharge the battery after it stops. This is a faulty Alternator.
Good luck.
 
  #5  
Old 03-17-2019, 04:17 PM
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Join Date: Mar 2019
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Bluegrass

Thanks,
I will give this a try and let you know how it goes.
 
 


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