Electrical Short

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  #1  
Old 10-03-03, 04:27 PM
KneelandRE
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Electrical Short

I have a 1996 Pontiac Grand AM that periodically shorts out. The dash light flicker a few times, and the all electrical power is gone. After waiting a few minutes it can be started up and run. This happens more often when it's damp or raining, but has also happened when it is dry. Any ideas where to start?
 
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  #2  
Old 10-03-03, 07:16 PM
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What you are describing should not be described as a "short" A short can be a path to ground or voltage. If your dash lights keep going out, you have an intermittent open most likely. Check the dimmer switch and the instrument panel grounds.
 
  #3  
Old 10-04-03, 06:08 AM
Joe_F
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As suggested, pick up a good wiring diagram from Alldata.com or a shop manual and check each ground.

Make sure to look at Alldata.com for any bulletins/trouble spots.
 
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Old 10-04-03, 10:39 AM
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I'd start with the battery terminals...
 
  #5  
Old 10-04-03, 03:38 PM
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I agree with BigGuy. If your losing BOTH, the ignition circuits AND the lighting circuits, you need to start looking at the battery terminals and work backwords.
 
  #6  
Old 10-04-03, 03:52 PM
macko
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Battery terminals would not cause you to loose all electrical power. The alternator would continue to provide power. Look for loose or rusty connections at the starter. This is where all the main fusable links are located. if they are good look for a ground problem. follow the negative lead to the engine block to start.

Macko
ASE Master Technician
 
  #7  
Old 10-05-03, 08:40 AM
Joe_F
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Macko:

Sure it would. Just ask the lady with the 1995 Neon that came to us some time ago with a "No start, nothing" condition. Towed the car in tearfully on a Saturday afternoon.

I was helping my neighbor do something and working on my 84 Oldsmobile at the shop that Saturday and he asked me to have a look.

I found a totally loose battery cable. Tightened it and it started right up. Called the lady up, she took the bus to the shop and explained to her what we found. She gladly paid a small fee, shook our hands and left. Problem solved.

I found it in 2 minutes.
 
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Old 10-08-03, 03:33 PM
matm347
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Starting a car is not the same as keeping a car running.

Once the car is running, the alternator both charges the battery, and runs the car. A well known test for an alternator is to disconnect the battery after the car is running.

I agree with Macko on this.
 
  #9  
Old 10-08-03, 08:55 PM
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Pulling the battery cable with the engine running sure does test the system.... Alternators and PCMs' just LOVE to have that huge voltage surge. That's the best way to kill an alternator.

Might want to check to see if the positive post is leaking on the battery(common problem).

Not sure if it applies to Grand Am's, But there was a bulletin on some GM V6's for an alternator ground problem.
 
  #10  
Old 10-09-03, 05:23 AM
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YEAH I DON'T THINK IT'S THE LOSS OF BATTERY VOLTAGE SO MUCH AS IT IS THE LOSS OF HAVING THE BATTERY CUSHION THE ALTERNATOR OUTPUT.
 
  #11  
Old 10-09-03, 06:41 AM
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matm347,

You are right about one thing,
"...A well known test for an alternator is to disconnect ...."

That is a 'Well Known' test.

But it is an obsolete test, hence, not performed any more.

The next best test I can think, to perform a quick 'no tools' test, is to rev the engine and watch the dash board charge indicator. If the bulb grows brighter when rev'ed, then the battery is dead. If the bulb grows dimmer when rev'ed, then the alternator is the problem.

However, this is not reliable all the time, so the old multimeter is the 'other' well known test.
 
  #12  
Old 10-09-03, 07:03 AM
Joe_F
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Exclamation

Once the car is running, the alternator both charges the battery, and runs the car. A well known test for an alternator is to disconnect the battery after the car is running.
----

If the car has anything computerized, you've just finished it off as FP stated. Never, ever do this. Not a valid test and tells you nothing.

ALWAYS use a DVOM to check for charging system problems as this is the correct way and will not fail you (or damage anything).
 
  #13  
Old 10-09-03, 08:20 AM
matm347
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I agree, don't do it...not to a new car....I was just trying to let them know that the battery no longer provides any voltage. DVOM is the best way.

Also, using jumper cables is another NO NO....CPUs don't fancy voltage drops/spikes.

I appologize for leaving the "don't do this" out of my previous post.
 
  #14  
Old 10-09-03, 09:24 AM
Joe_F
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I suppose even on an older car, you could fry the alternator diodes as they are one way passageways for juice.

Bottom line is that a DVOM in all cases gives you much better assessment than any quickie test....
 
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