Where/how Do I Look For A Short?

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.

 

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.

 

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.

 

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.

 

I’ve aways heard to disconnect the battery before welding.

 

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.

 

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.

 

I added to the above post; please read it again if you have already read it.

 

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

 

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?

 

BTDT.

 

Well....The Jeep was Dead again this morning. I definitely didn't leave anything on so I got a problem somewhere.

 

The most common source of a slow leak is the alternator. Start testing.

 

My first thought also. A bad diode will feed back.

 

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.

 

is the light on in glove box

 

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.

 

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.