# How do you find an electrical short?



## 1972_Stingray (Jan 30, 2005)

I just bought a 1989 F250 XLT Lariat with a 460 in it (don't know if any of that info helps) and about a week ago the battery seems to die within a day after charging it.Everyone tells me I have a bad short in it somewhere,but how do I find it?


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## batty_professor (Jul 29, 2004)

It will probably not be a short, but rather a small load remaining on when it shouldn't , such as perhaps a glovebox lamp as an example. You should place a low range ammeter in series with the positive battery terminal to battery, to see how much is being drained. Small currents 100 ma or less are acceptable and expected as this small current is what keeps the memory alive in the radio. Larger drains would indicate a problem. I'm suggesting the current test to verify there really is a problem, and not just a defective battery that won't hold a charge.


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## Guest (Jan 30, 2005)

Hi,

I agree with Batty on this one. Another thing you might look at, some times there are batteries that charge fully and appear to be O.K., but they simply will not hold a charge. 

I do doubt if it would be the alternator if it dies that quickly. Try the short thing, but also make sure it will hold a charge when unhooked. For a battery that will not hold a charge, a couple of starts with an engine that large, just do them in if they won't hold the charge.


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## 1972_Stingray (Jan 30, 2005)

The battery is brand new because I thought that might've solved it.I have had problems with the power windows (not going down all the way or not working at all). Could that have anything to do with it?


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## batty_professor (Jul 29, 2004)

Ok check the alternator. The system should support itself if the battery is disconnected while the engine is running. If this kills it, alternator isn't working. Don't forget to inspect the alternator connections before calling it dead.

The sluggish P/W's are definitely a clue here.


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## Volt-Schwibe (Jan 12, 2003)

i would do the ammeter test on the battery terminal and see what sort of a drain you have going on there.

if there's a big drain, you will want to find it.

if you find a large drain, pull the fuses one at a time, and check to see if the drain goes away.

if it doesn't go away no matter what fuse you pull, it is probably the alternator having a problem, and leeching power after the car is off.

with the fuses pulled, the only things that should be connected to power are the starter and alternator, and the alternator has the regulator inside of it. it is the regulator that can sometimes go bad, and drain your battery.

(once i had a datsun truck that had this problem really really bad, and it turned out that it was simply easier to put a battery switch on the car and forget the problem.)


also, make sure yours isn't one of the ones that were just recalled for a cruise control switch that will burst into flames.


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## Midnight Tech (Dec 31, 2001)

batty_professor said:


> Ok check the alternator. The system should support itself if the battery is disconnected while the engine is running. If this kills it, alternator isn't working. Don't forget to inspect the alternator connections before calling it dead.
> 
> The sluggish P/W's are definitely a clue here.


Make sure while disconnecting those cables you remove the negative first and replace it last. Doing it backwards is inviting a nice spark and possible explosion. Also don't disconnect EITHER cable with the engine running; it creates a surge in the electrical system that has the potential to damage a LOT of stuff...  
I'd take the alternator off and have your local parts store check it on an off the vehicle tester.


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## batty_professor (Jul 29, 2004)

Midnight Tech said:


> Make sure while disconnecting those cables you remove the negative first and replace it last. Doing it backwards is inviting a nice spark and possible explosion. Also don't disconnect EITHER cable with the engine running; it creates a surge in the electrical system that has the potential to damage a LOT of stuff...
> I'd take the alternator off and have your local parts store check it on an off the vehicle tester.


 That surge is minimized at an idle, and if the alternator is dead, there is no surge whatsoever. But you are correct that there is an expected surge if the system is working. The regulator "hunts" and the voltage gets squirrely. I've not seen this do damage from experience, but I appreciate your caution. The other "quickie" alternator indication is to place a ferrous metal object at the rear bearing housing of the alternator and feel for magnetic "pull". The rotor is a spinning electromagnet, and if all is working, the magnetism is easily detected. :smile:


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## Midnight Tech (Dec 31, 2001)

batty_professor said:


> The other "quickie" alternator indication is to place a ferrous metal object at the rear bearing housing of the alternator and feel for magnetic "pull". The rotor is a spinning electromagnet, and if all is working, the magnetism is easily detected. :smile:


 :sayyes:


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