Short or Open Circuit Troubleshooting
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3rd Gear
Joined: Jul 2008
Posts: 3
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Short or Open Circuit Troubleshooting
My 1985 C4 has a short or open circuit that will drain my new completely charged battery in 1-3 days when I leave it connected. I was wondering if there were any obvious issues with a short that I'm having. I have used a test lamp beween the positive cable and positive post on the battery while removing every fuse one by one to see if there is an obvious open circuit somewhere. I have not had any luck. Any help would be appreciated...
Pro
Joined: Jun 2008
Posts: 610
Likes: 1
Do you have an ammeter? I think it would be more revealing to use one instead of a test light when you do your fuse-pulling diagnostics.
A common cause of what you are seeing (in any kind of car) is a small light staying on all the time. I'd also try pulling the main wire from the alternator to see it that is the source of the draw.
A common cause of what you are seeing (in any kind of car) is a small light staying on all the time. I'd also try pulling the main wire from the alternator to see it that is the source of the draw.
Melting Slicks
Joined: Feb 2008
Posts: 3,286
Likes: 6
From: Palm Beach
Open circuits draw no current. You don't have an open. A short draws a lot till the fuse blows or the wire melts. As mentioned, you probably a component that is staying on and causing the draw.
Safety Car
Joined: Jul 2004
Posts: 3,845
Likes: 30
..before you start pulling your hair out trying to chase down the problem, be absolutely sure that your battery does not have a shorted cell which WILL give you the same symptoms you are experiencing, regardless if the battery is new or not..have your battery LOAD TESTED before you start chasing a problem that may not actually exist.....
Drifting
Joined: Sep 2003
Posts: 1,363
Likes: 7
From: 1994 LT1 Coupe 6-speed with FX3 & 2000 LS1 Vert 6-Speed with F45 Hunterdon County, NJ
agree with others, not an 'open', and also not a 'short' as it would blow a fuse or fusible link.
Most likely something simple or stupid. Here are a few common items:
At night, look inside the car and take note of any illumination (light left on, bad door switch leaving lights on, radio not turning off, etc).
Next in a quiet location, listen for any noise from under the seats (seat motor or switch on).
Next listen for noise in the rear hatch area for a clicking noise -- antenna circuit breaker resetting as antenna motor not turning off during the lowering of the antenna.
Most likely something simple or stupid. Here are a few common items:
At night, look inside the car and take note of any illumination (light left on, bad door switch leaving lights on, radio not turning off, etc).
Next in a quiet location, listen for any noise from under the seats (seat motor or switch on).
Next listen for noise in the rear hatch area for a clicking noise -- antenna circuit breaker resetting as antenna motor not turning off during the lowering of the antenna.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
battery drain
I just replaced the diode bridge in my alternator as one of the diodes was bad, and draining the battery in about a week.
You have the 140 amp alternator, and it would require some detective work to get the proper diode bridge because yours is the BIG alternator, and the larger components.
Try removing the battery lead from the alternator, and putting the lead in a plastic bag, and add masking tape to insure it doesn't puncture the bag, and short out. Check the battery over night, and see if the battery voltage is still up.
If it's up in 3 days, you have your culprit.
By the way, they are ex-pen-sive!
You have the 140 amp alternator, and it would require some detective work to get the proper diode bridge because yours is the BIG alternator, and the larger components.
Try removing the battery lead from the alternator, and putting the lead in a plastic bag, and add masking tape to insure it doesn't puncture the bag, and short out. Check the battery over night, and see if the battery voltage is still up.
If it's up in 3 days, you have your culprit.
By the way, they are ex-pen-sive!
