Battery discharge dilemma
Thread Starter
Racer
Joined: Feb 2008
Posts: 316
Likes: 0
From: Warwick Rhode Island
Battery discharge dilemma
I have to disconnect my postive terminal on my battery each time I park my 79. It seems that something's drawing on the battery even when it's not running. It's to the point that if I leave it hooked up it would be dead after 8 hours or so...
Has anyone come across this problem? If so, what was your solution. I'm afraid I might have a short somewhere.
Has anyone come across this problem? If so, what was your solution. I'm afraid I might have a short somewhere.
Melting Slicks
Joined: Mar 2007
Posts: 2,100
Likes: 12
From: Frederick Maryland
First...for safety you should disconnect your negative cable. There's a much greater chance of a spark from disconnecting the positive cable first. If there's any concentration of vented battery gas over the battery it could cause an explosion.
Now, for your problem. These issues are not uncommon on C3's. What you can do is leave the negative cable off the battery and attach a 12v test light to it. Have everything turned off and the doors closed. If the test light is still on, you have a discharge. If not, you may have a bad battery.
If the test light confirms a discharge, remove one fuse at a time. When the test light goes out you've isolated the circuit that's causing the problem. Then you can look for shorted wires, bad grounds, etc.
If you have a multimeter you can do the same with more accuracy.
Does your '79 have the courtesy light option? If so, the timer could be bad. It happened to the '78 I owned. It would not turn the courtesy lights off at times and would also turn them on at random, running down the battery. I replaced it and no more problem.
Now, for your problem. These issues are not uncommon on C3's. What you can do is leave the negative cable off the battery and attach a 12v test light to it. Have everything turned off and the doors closed. If the test light is still on, you have a discharge. If not, you may have a bad battery.
If the test light confirms a discharge, remove one fuse at a time. When the test light goes out you've isolated the circuit that's causing the problem. Then you can look for shorted wires, bad grounds, etc.
If you have a multimeter you can do the same with more accuracy.
Does your '79 have the courtesy light option? If so, the timer could be bad. It happened to the '78 I owned. It would not turn the courtesy lights off at times and would also turn them on at random, running down the battery. I replaced it and no more problem.
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
A fellow member Roger wrote this paper on finding the source of battery drains. Read it, try it, and see if it narrows it down any. Basically you're disconnecting the ground cable, and connecting a test light between the cable and the negative post. The light will light if there is a draw. Then you start pulling fuses one by one until the bulb goes out and you can narrow it down to that circuit. You can also, while the bulb is lit, disconnect items like the courtesy light, various relays that may have stuck, and even the plug in the alternator.
http://photos.imageevent.com/durango...%20Testing.pdf
Hope this helps a little bit.
http://photos.imageevent.com/durango...%20Testing.pdf
Hope this helps a little bit.
Melting Slicks
Joined: Dec 2006
Posts: 2,669
Likes: 3
From: Kingston Ontario
You're right DB, Roger's elect test is bang on! Have not heard from Roger in some time now, like Dec 07.
Follow his test to the letter and it should solve the problem or at the very least isolate to one circuit.
Follow his test to the letter and it should solve the problem or at the very least isolate to one circuit.
Drifting
Joined: Jan 2008
Posts: 1,962
Likes: 5
From: Schererville IN
My question is why should we put the quick disconnect on the negative vs the positive side of the battery? I installed on the positive cable as there was more room in that vacinity to put it. It works fine there. Due to the draw, I get a spark when re-connecting no matter wich post it's connected to. With or without the short, we are completing the circuit the same either by touching the positive or negative post, thus a spark. What's the difference? Why is negative safer than positive?
Last edited by blckslvr79; Feb 21, 2008 at 01:29 PM.
Melting Slicks
Joined: Dec 2006
Posts: 2,669
Likes: 3
From: Kingston Ontario
Same issue here-my battery will drain down within about 4-5 hours to the point it won't crank the car. I installed a quick disconnect till I have the time to find the little demon.
My question is why should we put the quick disconnect on the negative vs the positive side of the battery? I installed on the positive cable as there was more room in that vacinity to put it. It works fine there. Due to the draw, I get a spark when re-connecting no matter wich post it's connected to. With or without the short, we are completing the circuit the same either by touching the positive or negative post, thus a spark. What's the difference? Why is negative safer than positive?
My question is why should we put the quick disconnect on the negative vs the positive side of the battery? I installed on the positive cable as there was more room in that vacinity to put it. It works fine there. Due to the draw, I get a spark when re-connecting no matter wich post it's connected to. With or without the short, we are completing the circuit the same either by touching the positive or negative post, thus a spark. What's the difference? Why is negative safer than positive?
Drifting
Joined: Jan 2008
Posts: 1,962
Likes: 5
From: Schererville IN
I know that. It's a real pain in the ****. I had no issue till I redid the interior. My bet (without testing yet) is that its either the glove box light shorting out or the dome light switches as I messed with these when installing speakers in the kick panels. Finding this Gremlin is at the top of my list when spring comes.
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Same issue here-my battery will drain down within about 4-5 hours to the point it won't crank the car. I installed a quick disconnect till I have the time to find the little demon.
My question is why should we put the quick disconnect on the negative vs the positive side of the battery? I installed on the positive cable as there was more room in that vacinity to put it. It works fine there. Due to the draw, I get a spark when re-connecting no matter wich post it's connected to. With or without the short, we are completing the circuit the same either by touching the positive or negative post, thus a spark. What's the difference? Why is negative safer than positive?
My question is why should we put the quick disconnect on the negative vs the positive side of the battery? I installed on the positive cable as there was more room in that vacinity to put it. It works fine there. Due to the draw, I get a spark when re-connecting no matter wich post it's connected to. With or without the short, we are completing the circuit the same either by touching the positive or negative post, thus a spark. What's the difference? Why is negative safer than positive?
Try the test light procedure and try disconnecting things that are hardwired to the battery. Try everything. The alternator plug, the horn relay, the harmonica connector under the steering column, the courtesy light timer, the seatbelt warning buzzer relay...you get the idea. The point is to pull all of these items one at a time until the test light goes out. Someone on a different thread pointed out that a bad alternator diode can even cause a fast battery drain.
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Drifting
Joined: Jan 2008
Posts: 1,962
Likes: 5
From: Schererville IN
Also-How do you know if your car has the delayed courtesy lights?
Mine is a 79 L82 pretty well loaded with options, but my interior lights turn off right away. Where is the relay that delay the lights located? What am I looking for?
Mine is a 79 L82 pretty well loaded with options, but my interior lights turn off right away. Where is the relay that delay the lights located? What am I looking for?
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
It's behind the driver's side knee pad dash. I don't know what it would look like because the silver canister, basically a LONG signal blinker, was last used in '77. I do know it's a two terminal plug on a pigtail with a ground wire leading off of the canister. Mine was too high to get to from under the dash...I had to loosen the panel and pull it away from the A-pillar to get to mine.
Thread Starter
Racer
Joined: Feb 2008
Posts: 316
Likes: 0
From: Warwick Rhode Island
Battery discharge dilemma
Thanks for the quick replies. I will perform this test and see what shakes out. I do have the courtesy light option - my lights in the footwells stay on approximately 30-45 seconds after I shut the doors. I didn't notice if the overhead light stayed on. I'll check that as well. What I also realize is that my horn doesn't work. I'm wondering if there's a short or if the problem is coming from this in some way. I'll perform that test and let you know how it goes.
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
Same issue here-my battery will drain down within about 4-5 hours to the point it won't crank the car. I installed a quick disconnect till I have the time to find the little demon.
My question is why should we put the quick disconnect on the negative vs the positive side of the battery? I installed on the positive cable as there was more room in that vacinity to put it. It works fine there. Due to the draw, I get a spark when re-connecting no matter wich post it's connected to. With or without the short, we are completing the circuit the same either by touching the positive or negative post, thus a spark. What's the difference? Why is negative safer than positive?
My question is why should we put the quick disconnect on the negative vs the positive side of the battery? I installed on the positive cable as there was more room in that vacinity to put it. It works fine there. Due to the draw, I get a spark when re-connecting no matter wich post it's connected to. With or without the short, we are completing the circuit the same either by touching the positive or negative post, thus a spark. What's the difference? Why is negative safer than positive?
So, having said that, Yes Rogers paper covers the troubleshooting procedure rather well.
If your killing the battery in 4 or 5 hours you have a Very big drain somewhere, Likely candidate is the ground wire that is supposed to be connected to the starter, but frequently gets connected to the + cable on the starter. Look there first. It comes from the wire harness on the firewall down towards the starter, its black with a large ring terminal on it and is supposed to be on the bellhousing bolt.
Racer
Joined: Mar 2006
Posts: 276
Likes: 1
From: Pistoia PT (ITALY)
99% of the problem can be the big capacitor of the delay courtesy lamp circuit!
Is not uncommon for a 20-30 years old capacitor to have some parassistic lost in the dielectric.
The risult is a small current drain (due to the internal lost od insulation of the capacitor) able to discharge your battery in 10-12 hours...... not totally, but enough to don't ba able to start the engine.
This is my esperience in my 79 Corvette!
Is not uncommon for a 20-30 years old capacitor to have some parassistic lost in the dielectric.
The risult is a small current drain (due to the internal lost od insulation of the capacitor) able to discharge your battery in 10-12 hours...... not totally, but enough to don't ba able to start the engine.
This is my esperience in my 79 Corvette!
Melting Slicks
Joined: Nov 2003
Posts: 2,668
Likes: 119
From: St. Charles Mo
CI 5 & 8 Veteran
It does not matter which terminal on the battery is connected first. The probability of sparking is equal. The main reason we always switch the positive side is safety. We don't want voltage spread thru-out the system where an inadvertent short to ground will cause high current load.Bullshark
Race Director
Joined: Apr 2007
Posts: 14,062
Likes: 602
From: Henderson Nv-Rohnert Park/Sonoma C o. ca/born in NY Rockaway Beach.
99% of the problem can be the big capacitor of the delay courtesy lamp circuit!
Is not uncommon for a 20-30 years old capacitor to have some parassistic lost in the dielectric.
The risult is a small current drain (due to the internal lost od insulation of the capacitor) able to discharge your battery in 10-12 hours...... not totally, but enough to don't ba able to start the engine.
This is my esperience in my 79 Corvette!
Is not uncommon for a 20-30 years old capacitor to have some parassistic lost in the dielectric.
The risult is a small current drain (due to the internal lost od insulation of the capacitor) able to discharge your battery in 10-12 hours...... not totally, but enough to don't ba able to start the engine.
This is my esperience in my 79 Corvette!
Drifting
Joined: Jan 2008
Posts: 1,962
Likes: 5
From: Schererville IN
Right on Sixfooter It does not matter which terminal on the battery is connected first. The probability of sparking is equal. The main reason we always switch the positive side is safety. We don't want voltage spread thru-out the system where an inadvertent short to ground will cause high current load.
Bullshark
It does not matter which terminal on the battery is connected first. The probability of sparking is equal. The main reason we always switch the positive side is safety. We don't want voltage spread thru-out the system where an inadvertent short to ground will cause high current load.Bullshark
You can kill the ground to/from the battery, but your car is still being fed with hot current. Disconnecting the positive side with a switch just makes more sense to me.
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
There are technical reasons for disconnecting the ground instead of the positive , basicly the electrons "flow" from negative to positive, opposite of what most think. The practical reason for disconnecting the ground first is that if your wrench happens to touch something while it is also on the negative battery terminal, nothing happens. Then when you disconnect the positive it can touch the chassis or some other metal without sparking. All that said, unhooking either will keep your battery from discharging and the current only flows where there is a path.
Drifting
Joined: Apr 2007
Posts: 1,970
Likes: 45
From: Cameron Park CA
There are technical reasons for disconnecting the ground instead of the positive , basicly the electrons "flow" from negative to positive, opposite of what most think. The practical reason for disconnecting the ground first is that if your wrench happens to touch something while it is also on the negative battery terminal, nothing happens. Then when you disconnect the positive it can touch the chassis or some other metal without sparking. All that said, unhooking either will keep your battery from discharging and the current only flows where there is a path.
If you ground the wrench while disconnecting the neg. terminal no spark, no problem. Not so much of an issue on a C3 because of the battery location, but in general it's a good practice to disconnect the neg. first.Cheers,
Pete
