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Where/how Do I Look For A Short?

Discussion in 'Early CJ5 and CJ6 Tech' started by Buildflycrash, Apr 3, 2021.

  1. Apr 3, 2021
    Buildflycrash

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    Gulf Breeze FL...
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    Suddenly my battery is dead. 2yo top of the line NAPA Legend. I didn’t disconnect it and did a little welding on my tire carrier a couple days ago. Next day nothing. Jump it and it runs fine. Restarts after shutting down but in 15min it wouldn’t start. Overnight it’s completely dead.

    Did I fry something by welding? No other changes recently. I looked for crushed wires back by the tire carrier but I see nothing bad there.

    Where do I start? What do I do? Thanks.
     
  2. Apr 3, 2021
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Hills of NH
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    Start at the source. Disconnect the positive cable at the battery, check if the cable shows zero or near zero Ohms to ground. If so, you have a major short somewhere. An example might be the voltage regulator is stuck or fried. So then test each circuit individually the same way, say by removing fuses to isolate them.

    Also, I would give the battery a full charge overnight, then see if it holds the charge if disconnected from the vehicle.
     
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  3. Apr 3, 2021
    Buildflycrash

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    I have a multi-meter but don’t know Ohms. I understand it measures resistance but that’s about all. What is a good/bad number I have no idea.
     
  4. Apr 3, 2021
    PeteL

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    Zero ohms is perfect conductivity - in other words a full short. Check your meter by crossing the two test probes.

    Infinite ohms, or an extremely high number (thousands) is what you will see if there is no drain, or a complete break.

    Most healthy circuits, say a tail-light, if switched "on" will show a few ohms resistance (5 or 10 or 20?) as the bulb filament conducts to ground for example.
     
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  5. Apr 4, 2021
    Jrobz23

    Jrobz23 Member

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    I’ve aways heard to disconnect the battery before welding.
     
  6. Apr 4, 2021
    timgr

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    I would charge the battery overnight before I condemned it. Your local parts store will check the battery for you, but it should be fully charged. It should also be fully charged for the following test.

    I would also use the amps setting on my multimeter to check for some drain on the battery. Amps are a measure of electric current. Disconnect one battery cable and measure amps from the disconnected cable to the battery post. It should be nothing or a milliamp or two. Note that this is with EVERYTHING OFF. If you leave something on you could blow the fuse in your meter. Typically your meter will have one location for your lead that's say 10 amps, and another that's for smaller currents. Start on the higher scale.

    If you welded on the Jeep, it's possible to damage the semiconductors in your alternator or regulator. This could either keep the flat battery from charging, or make a path to ground that drains your battery.
     
    Last edited: Apr 4, 2021
  7. Apr 4, 2021
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

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    To go further with this, if there is a draw of more than a trace amount, start disconnecting one accessory at a time until the meter drops. Alternator, radio, ignition switch...

    Or if you have a fuse panel, you can do the same thing at each fuse. Remove fuse, test for amps between the posts. If no draw, replace.
     
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  8. Apr 4, 2021
    timgr

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    I added to the above post; please read it again if you have already read it.
     
  9. Apr 4, 2021
    Buildflycrash

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    I did charge the battery overnight with it disconnected. I let it sit for a couple hours this morning with no significant drop in voltage. Reconnected it and went for a drive A few minutes ago. I suddenly have a major death wobble issue but that’s a subject for another thread. I’ve been moving tires around and adjusted the toe in as I have a slight bend in my tire rod now from the jeep falling off the jack. I’m gonna let it sit for a while longer all connected with Nothing running. Then I will check the voltage and see how it starts. Will report back shortly
     
  10. Apr 4, 2021
    Buildflycrash

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    So far so good. Been sitting a couple hours after going for a ride this morning. Reading 12.7 on my digital dash gauge with the key on. Maybe I just left something on the other day and battery needed a full charge to maintain?
     
  11. Apr 4, 2021
    PeteL

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    BTDT.
     
  12. Apr 5, 2021
    Buildflycrash

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    Well....The Jeep was Dead again this morning. I definitely didn't leave anything on so I got a problem somewhere.
     
  13. Apr 5, 2021
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

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    The most common source of a slow leak is the alternator. Start testing.
     
  14. Apr 5, 2021
    PeteL

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    My first thought also. A bad diode will feed back.
     
  15. Apr 6, 2021
    Buildflycrash

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    Testing is hard so I happened to have a brand new single wire on my 231 (on engine stand). It was not the problem. Still losing power. I have the battery out and charging now. I’ll go by the parts store to test this evening.
     
  16. Apr 6, 2021
    Twin2

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    is the light on in glove box :whistle:
     
  17. Apr 6, 2021
    OldAdobe

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    If you don't have or want to use a multimeter then try using a test light. Same instructions as using a multimeter.
    Turn off everything, remove key, and Remove the positive or negative cable from the battery. Connect the test light pointy end into the battery post and then attach the alligator clip to the disconnected cable. If the testlight turns on then jiggle the ignition switch (don't start it!), turn off everything, pull chargers out of the cigarette lighter, pull fuses and relays until the light goes off.

    Oddest short that I've found was the tip of a brass screw on a fuse box was a bit too long. It had worn through the fuse base just enough to cause a drain but not blow a fuse, weird.
     
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  18. Apr 7, 2021
    Buildflycrash

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    Ready
    Fire
    Aim

    Fixing this with a Parts Cannon. New alternator didn't work so try a new battery next.
    Actually I had the battery tested and it said "replace" So I got a prorated $$ battery for $50.
    I installed it before work and I'm sure to know something in a bit when I get home.
     
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