Can't find that darn electrical short

[jaredawoodruff]

Hey there,

I have a 1998 T4R 6-cyl 4wd that's treated me great, even at 330k miles

EDIT

So I just tested Amperage while the engine is running with lights on, it's about 24 Amps, engine off with the lights on measures even less and I get a reading of 0.0 Amps with everything off. However I do get a very low voltage reading when the engine is on and when the alternator is supposed to be charging. When idling the headlights pulse and the engine RPMs change slightly until I give it gas. So is this possibly an alternator or voltage regulator issue rather than a draw? The battery still seems to die if I leave it plugged in under the hood, is the alternator maybe making a draw? Because the battery seems to be fine if I take it out. I'll try charging the battery and leaving it sit for a day to make sure it isn't faulty as well.

Lately an electrical short has been plaguing me and I can't find it for the life of me. The Alt and Voltage Regulator are good, the battery is good and none of the fuses are blown. When I hooked up my multimeter between the negative terminal and the negative connector, I get a 12V draw when everything is off. I even pulled EVERY fuse I could find and I still get the 12V draw. When I disconnected the positive terminal from the fuse box under the hood, the voltage reading dropped to about 5V or 6V. This one is stumping me pretty good. It takes about a day an a half without running it for the battery to drain to where it won't or almost won't start.

Has anyone else experienced this problem before? If so, I'd love to know what the problem was.

Thanks,
Jared

 

[jonwilly2]

Maybe the alternator isnt as good as you think. They are easy to open up and clean. I think its a bad cable end or cable. For a while my 4Runner was acting like it had a bad battery and after digging through everything; I had a bad positive batter end of the cable that goes to the fuse box and the ground was going out. After cleaning the alternator and putting on a new ground cable and positive cable end. My in cab battery meter always reeds 14 or 14.5 when its running and 12 to 13 off.

 

[jmt2404]

You could try taping a sewing needle to the multimeter prongs and then sticking the needle through each wire to ty and trace it back to the source... Just an idea.. not sure if it works or not.. never tried it.

 

[SST221]

Try switching your meter to AMP's. A "draw" is voltage being consumed which is measured in AMP's. Then try the fuse thing again based on the amount of amperage draw. So if its less than 1.0amp which it should be based on the time you stated, start with the smaller fuses.

 

[jaredawoodruff]

Try switching your meter to AMP's. A "draw" is voltage being consumed which is measured in AMP's. Then try the fuse thing again based on the amount of amperage draw. So if its less than 1.0amp which it should be based on the time you stated, start with the smaller fuses.

Thanks for the tip. I get a reading of 0 amps, but it won't measure in DC, only AC. Is that a problem?

 

[Baja Runner]

Yeah, about 12V is what you're supposed to read. A good battery should be more in the 12.75V range though.

Amps and Volts are 2 very different things. Volt is the potential for electrons to flow, and amperage is the amount of electrons moving.

If you're trying to see how much electricity the car is draining from the battery, you need to run your multimeter "in series" with the positive or negative battery post.

Diagram:
Chassis ground ---> (Ammeter) ---> Neg Battery terminal that is disconnected from the chassis ground location.

When measuring volts, you can place the volt meter in parallel. Most mulitmeters make you switch one of the probe wires on them so it doesn't short the meter itself.

Why do you think there is a draw? Most likely the battery is just old, and unable to hold a charge .

 

[SST221]

Yeah, about 12V is what you're supposed to read. A good battery should be more in the 12.75V range though.

Amps and Volts are 2 very different things. Volt is the potential for electrons to flow, and amperage is the amount of electrons moving.

If you're trying to see how much electricity the car is draining from the battery, you need to run your multimeter "in series" with the positive or negative battery post.

Diagram:
Chassis ground ---> (Ammeter) ---> Neg Battery terminal that is disconnected from the chassis ground location.

When measuring volts, you can place the volt meter in parallel. Most mulitmeters make you switch one of the probe wires on them so it doesn't short the meter itself.

Why do you think there is a draw? Most likely the battery is just old, and unable to hold a charge .

I agree, even 12.0v is considered bad. Six cells in a battery each @ 2.1v for a total of 12.6v. If your battery is say 5 years old I would put a battery in it anyways.

 

[pauls4runner]

do a google, or youtube search for parasitic draw test. depending on what style/type of DMM you have, set the DMM to read amps with the 10a selection. you then disconnect the negative battery terminal, one side of the meter, secure it to the negative battery post ( i rest the DMM probe against the post and wrap it with electrical tape) and the other lead, secure it to the negative cable end. wait a few minutes for all of the computers to go to sleep. once all the computers are asleep, you should have a reading on your DMM of .5A or less. also when doing this, make sure the key is not in the ignition, make sure all lights are turned off, close all the doors, I roll the windows down. once the DMM is inline set on amps, opening the door will turn the dome light on, the load for turnng the dome light on will draw enough current to blow the fuse in your DMM. if your DMM reading is over .5 their is a parasitic draw, thats when you start pulling fuses one at a time, after each fuse is pulled watch the DMM to decrease, once you pull a fuse and see the reading decrese, you will know what circuit your problem is in. Again, I strongly suggest doing a google or youtube search for "parasitic draw test" to get a well written, well done video explanation of the proper methods to do this

 

[jaredawoodruff]

I'll do some more tests tomorrow since it's dark right now. I think my Alternator may have a problem actually, it's now reading 12v while running if I have the head lights on :/

The battery should be fine, it's less than 3 years old. I rebuilt the alternator (just a new brush) last year, perhaps I may have done something wrong that turned into a problem now.

Updates will come tomorrow, thanks guys.

Edited the first post of the thread with new details.

-Jared

 

[Socco]

I'll do some more tests tomorrow since it's dark right now. I think my Alternator may have a problem actually, it's now reading 12v while running if I have the head lights on :/

The battery should be fine, it's less than 3 years old. I rebuilt the alternator (just a new brush) last year, perhaps I may have done something wrong that turned into a problem now.

Updates will come tomorrow, thanks guys.

Edited the first post of the thread with new details.

-Jared

You should be closer to 13.8v while running, regardless of the load. 12v while running with the lights isn't enough to keep the battery charged for long. Can you take the alternator to a local parts store that can test it for you?

If you have discharged the battery (ran it flat) too much, that will weaken it substantially. A load test is the only way to be sure of its condition. Again a local parts store should have a load tester to confirm.

Edit: Just noticed your unanswered question- You must measure current draw in amps DC. Measuring in AC will always show as 0 amps.