Battery or Alternator?
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Elder User
Joined: Feb 2007
Posts: 829
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From: Goose Creek SC
Battery or Alternator?
My "charging System Failure" light just lit. I should be able test the alternator by reading the battery while the truck is running?
Anything else it can be? Any other tests?
Thanks.....Bob
Anything else it can be? Any other tests?
Thanks.....Bob
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
You should get 13.5+ volts across the battery with a multimeter while the engine's running, and 12+ volts with the engine off. If you only get 12v or less with the engine running the alternator or it's internal regulator has failed.
P.S. If the alternator fails this test, and you take the alternator to a parts house and they test it on one of those quick benchtop testers and say it's good, ignore them and get another alternator anyway.
P.S. If the alternator fails this test, and you take the alternator to a parts house and they test it on one of those quick benchtop testers and say it's good, ignore them and get another alternator anyway.
Last edited by Conanski; May 31, 2007 at 02:27 PM.
Elder User
Joined: May 2007
Posts: 754
Likes: 1
From: Solon, Ohio
A fully charged battery sits at about 12.75 volts with the engine not running and everything turned off. It might be slightly lower on older or not perfect batteries.
With the engine running it should be 13.50 -16.00 depending on how much it's charging.
If it stays above 13.25 with the engine running and the headlights on, your alternator should be OK.
You might want to check your body ground by scratching a clean shinny spot on your fender inside the hood area, and measure from the center of the negative battery cable and that spot with the engine running and the lights on. It should read 0.00.
With the engine running it should be 13.50 -16.00 depending on how much it's charging.
If it stays above 13.25 with the engine running and the headlights on, your alternator should be OK.
You might want to check your body ground by scratching a clean shinny spot on your fender inside the hood area, and measure from the center of the negative battery cable and that spot with the engine running and the lights on. It should read 0.00.
Freshman User
Joined: Feb 2007
Posts: 32
Likes: 0
From: Topeka, KS / Okmulgee, OK
Go to harborfreight.com and order yourself a battery load tester they also have a function for testing the charging system. as cheap as they are they make life a whle lot easier. Mine earned its place in my toolbox the first time i used it.
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