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Detecting a Short on A 1992 GMC Sierra
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kkanuck
New User
Dec 6, 2007, 9:51 AM
Post #1 of 3
(4442 views)
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Detecting a Short on A 1992 GMC Sierra
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Hello to all,
I am brand new here, and look forward to learning lots....
I was wondering if anyone can point me in the proper direction to narrowing my problem down. I am an electrician, so circuits / wiring are no problems, I just would like to find out the easy method to trace.
I find that the battery will drain over time, like a small short is draining the battery.
I was charging the battery yesterday with a charger, hooked up to the battery which was wired to the vehicle. I moved the charger units location in the engine compartment and the housing of the charger (which is grounded to house A/C current via the extension cord) bumped the chassis of the vehicle, which is grounded to the battery and I saw a nice spark. It was charging at the time, so not sure if that makes a difference???
What I need to know, is if I do have a short, can it drain the battery while one is driving and the generator works no worries? Can it cause any bad damage or is a slow battery drain when vehicle is off the worst of my issues?
If I use one of those small test lights, do I pull each fuse and put the tester with light's probes to each side of the fuse holder, and the one fuse holder that makes the light turn on is the circuit with the issue?
Cheers for any troubleshooting tech advice on this,
Many Thanks in advance,
Tibor
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Dec 6, 2007, 11:49 AM
Post #2 of 3
(4437 views)
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Re: Detecting a Short on A 1992 GMC Sierra
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If your charger with house current made a spark to body ground of car that should only hurt the charger. You can use a regular test light for fuses to see that both side light up which checks a fuse but wouldn't tell you if there was a drain.
There is some milleamps of drain that is normal and wouldn't be noticeable that is really just maintaining memory in things in the vehicle.
A battery can drain itself without help - fairly rare but if it is left disconnected and doesn't hold a charge it's toast by itself. That is a little rare but happens. Regular lead-acid automotive batteries do lose dependablity after about 3 years old yet you will hear of ones much older doing fine.
You can check for a drain that does leave you with a dead battery overnight or two by just hooking up a common test light with a bulb between bat neg terminal and the disconnected neg cable. It should not light a test light. There would be some minute draw but not enough to light the light. If the light doesn't light up I suspect the battery itself. Batteries are marked as to how old they are usually with a letter and # like B-4 which = February of 2004 as date of manufacture. Some have codes that are hard to decifer embossed in the battery and if tricky you can ask at a place that sells that brand when it was made.
If the test light lights up you can then shut everything in the vehicle off and don't forget hood lights, interior lights etc. Pulling one fuse at a time you will probably pull one that make the test light go out. The problem is in that circuit. Doesn't tell you what but isolates the prob to that circuit. Delayed interior light screw up this trick so that may show as a short and just be misleading. Defeat that by pulling the fuse or whatever to shut them off.
Things that happen are glove box lights and other compartment lights that should shut off might not for some reason and you don't see the light staying on in those so pull bulbs or if you find the switch for those items press it to off with it open like you can with most refrigerators that people have at home.
It doesn't take all that much to bring a battery down. You would thing a small bulb in a glove box wouldn't do it but they can. The constant discharging and recharging of the vehicles battery is hard on it and makes the alternator work VERY hard after a jump and many can fail from trying too hard, too often.
When you have the engine running the alternator should be able to overcome any assesorie the vehicle has and should read a voltage of about 13.8 or so. If it can't the alternator is not putting out enough amps. If it reads much lower than that the drain is fairly strong and would kill the battery in a short time when engine is off.
The alt can be the drain itself. There is one main power wire to it from the battery and if the test light test mentioned makes the light go out with that main feed to the alternator its highly likely the alternator itself is the problem.
You can buy parts for the alternator or a replacement should cover all the defects possible.
So: If you find a circuit that drains with pulling fuses find out what that fuse covers and let the hunt begin. Almost all drains will be a problem with a circuit that is empowered when vehicle is off and keys are out. Item that stay empowered are horns, brake lights, hazzard lights, power ports/lighters interior and convenience lighting, and possible power seats and a few other things that I can't think of right now.
See what you can find and hit back. If still confused - join the club of the folks that have confusing electrical problems with motor vehicles and the hair loss they can cause,
T
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kkanuck
New User
Dec 6, 2007, 1:13 PM
Post #3 of 3
(4436 views)
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Re: Detecting a Short on A 1992 GMC Sierra
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Hi Tom,
I thank you very much for the tips.......I will hunt this down and report back later.....
Cheers,
Tibor
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