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  #1  
Old January 10th, 2011, 08:53 PM
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Bradlee Duncan
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Electrical troubleshooting advice

Hi all,
Ever since I completed the rebuild of the D-90, I've been having a problem with the electrical system. There is a definite drain going on somewhere and it's slow enough that the battery will last about 4 days. If I try to start it on the 5th day the battery won't have enough juice to turn the engine over.

So, the question is, (since I'm handy but not an electrician), how do I go about narrowing down the culprit? I'm sure I've just missed some wire somewhere but I've scoured the wiring diagrams and can't seem to find anything substantial. I think it's related to the alternator somehow because when the engine is off, there is a definite electrical sound/buzz from the alternator area. I just can't figure out why. Any advice as to what it might be or how one might troubleshoot electrical problems is welcomed!
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  #2  
Old January 10th, 2011, 09:02 PM
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Jeff Huff
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I am struggling with a similar problem but in my case I have found that my alternator is only putting out about 35 amps under load so it isn't charging the battery...how are you verifying that your battery is good and fully charged before the start of the 4 day countdown?
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Old January 10th, 2011, 09:56 PM
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Alden
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my 2c

Probably it's your battery. if not,
I'd try unplugging the known systems that could possibly drain the battery - radio, winch, alarm, ??
Either leave them unplugged and see if it still drains, or use an electrical meter to check the change before and after.
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  #4  
Old January 10th, 2011, 10:56 PM
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Bradlee Duncan
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It's a brand new battery, so I'm pretty sure I can mostly rule that out but I haven't confirmed that it's completely charged when I start the 4-day count down. One time I did put a charger on it overnight to make sure it was charged in the morning. The simple check on the charger says that the battery was good, but I don't know how sophisticated that is.

I was thinking of trying to unhook certain systems but I don't have a winch, radio, or alarm, yet. The only thing other than the heater, lights, and ignition system is the electrical fans that I installed. But I also tried unhooking them and it still drains so it seems I've ruled those out too. I'm really stumped but I'd like to know why the alternator still makes a buzzing/electrical sound when the ignition is off something tells me if I can get it to stop making the buzzing-type sound then I could get the battery to hold a charge. Thanks for the help guys, I'll try to rule some more things out.

Does anyone know how I could check the alternator? Is it as simple as running the engine and then using a multi-meter to measure the amperage coming out?
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  #5  
Old January 10th, 2011, 11:10 PM
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kevin
1994 D90 300tdi #730, SIII 88
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Your alternator's field is energized, check your ignition switch and circuit.
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  #6  
Old January 11th, 2011, 11:40 AM
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Bradlee Duncan
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Interesting, can you expound on how I can do that? I read something last night along these lines that says a part inside the alternator can go bad basically allowing current to flow in the wrong direction when the alternator is not spinning, thus draining the battery. Is this the same thing that you're saying or is this something different? Thanks for the help!
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  #7  
Old January 11th, 2011, 11:50 AM
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kevin
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It's more common for it to be a faulty ignition switch, but there are a few other causes as well.
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  #8  
Old January 12th, 2011, 08:13 AM
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Gren Thomas
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alternator x2

mine went south and would drain the battery but it would also charge it, however if it was left for a few days the batt would be flat as a fart.

try disconnecting the live feed from the alt to isolate it but make sure you leave the battery connected to the rest of the trucks circuits.

also did you pull any perminently live cables through the frame?
next thing is to pull fuses to isolate the problem curcuit.

have you checked the current draw when the ign is off.

have fun

Gren
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