Testing for an electrical short

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340Dart

340Dart

Obsessive Dart Disorder
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I went to start my car and the battery was low and wouldn't turn the engine over. Battery was checked and is good. Somebody told me that there is probably a short draining the battery. They told me to take 1 cable off the battery and hook the test light clip to the cable and the point of the test light to the terminal. If it lights, there is a short somewhere. Is this the correct way to test it?

Fred B
 
The test light will tell you if there is some current draw that is large enough to light the bulb...you will want to do this on the positive cable. That won't help you find it though.

With all the cold weather we've been having, it may have just gone flat from a minor current draw/age if you're not using a float charger. I'd get something like a battery tender. If you had a problem, it will do this in the summer time.
 
Better to use the ground cable rather than positlve. That way if you touch something it won't short something, "like your wrench"


You make certain everything is shut off, check for things like dome, map, trunk lamps.

Remove the battery ground, and hook one end of your test lamp to a good ground. Stab the probe of the test lamp into the battery NEG post. If it lights you have a drain. Look carefully in dim light, because a "slight" drain may barely light the lamp, or not at all.

Really. And I mean REALLY, if you have one of these old girls, you should spend 30 bucks or so and buy yourself a multimeter and a bag of clip leads from Radio Shack. Make sure the meter you buy has some DC current scales, and can read current up to at least 10 amps.

After you check with a light and determine that it does NOT light, now it's safe to check with a multimeter. Same deal as the lamp. Set the meter up for DC current, and start with the largest scale, 10 amps, 20 amps whatever. If you do not get a reading, set the meter up for less current and recheck.

If you post a meter you are interested in, that is the model and brand, we can guide you as to whether it's got the appropriate scales
 
If your light/meter shows that there is a draw have someone watch the light/meter and pull the fuses one at a time until the draw goes away. This will help narrow your search to a certain circuit. If the draw doesn't go away it may be in the charging circuit, then unhook the alternator. Remember that if you pull the fuses with the door open your dome light will cause a draw (remove the dome light bulb).
 
Parasitic draw on these OLD cars should be near 0 amps .... PERIOD .... test light OLD school ... get yourself an updated ammeter with pickup that you can clip to negative cable ... this will tell the whole story ...
 
rrvolare said:
Parasitic draw on these OLD cars should be near 0 amps .... PERIOD .... test light OLD school ... get yourself an updated ammeter with pickup that you can clip to negative cable ... this will tell the whole story ...
Click to expand...


I always and I still recommend that you START with a test lamp. This is because if the draw exceeds the current range of your multimeter,.................especially someone who is not that familiar..............you can pop the ammeter fuse IF it has one. Fluke ammeter fuses are NOT cheap. Some meters are not fused, and may not have protection.
 
Well the test light went on. So I guess I have a short. I have a Fluke 73 multimeter. So I will have to start checking to see where it is. I will try pulling one fuse at a time and check it. Thanks for all the replies.

Fred B
 
You have a drain, you may or may not have a "short." Really, two different things.

As suggested above

Make certain everything is off, EVERYTHING

Pull fuses one at a time

If that does not kill the lamp, unhook the alternator stud (output) and tape off the wire

If that does not kill the lamp........

Do you have a separate stereo amp? Problems in the output circuit of those can cause a draw.
 
Less than half of the fuses are hot with the ignition switch off so pulling all the fuses may be a waste of time. If the brake lamp switch is bad or out of adjustment the brake lights would stay on and kill the battery. Same applies to a door jamb switch or rotated head light /dome light switch.
If had to guess where the draw is... 1st guess would be inside the alternator. Second guess is inside the starter.
The above is based on my experience with every type of vehicle and not just your a-body. hope it helps
 
You may also want to check your glove box lamp at night to see if it stays on with the door closed thus pulling enough current to drain the battery after a couple of days.
 
Well finally got to check it out. It turned out to be my Kenwood stereo unit. Pull the power wire off test light goes out. Thanks for all the help.

Fred B
 
hmmm, stereo memory/clock is hot at all times and would dimly light a test lamp. It isn't enough drain to harm a decent battery unless its over a long period.
 
I had trouble with the stereo towards the end of summer. So there was something defiantly wrong with it. Test light was bright until I take off power wire. Now no more draw.

Fred B
 
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