Tracking Down a Voltage Draw

[Travis Munday]

Recently my truck has been giving me problems: the battery doesn't want to stay charged. With the battery charged (via a charger) and hooked to the truck, it will last only a few days before there is not enough juice to turn the truck over; however, with the battery fully charged and disconnected from the truck, a week later, the battery is still strong.



My guess is that something is drawing current and draining the battery, so I've been trying to track down the culprit circuit. I just removed every single fuse and relay (side of dash, underhood, and aftermarket) one at a time and still would show 12V to ground (battery disconnected, measuring from negative battery terminal to negative battery lead).



The fuse for the dome light was removed, so having the door open had no effect on readings. Is there a combination of fuses that will kill power to the computer, radio, and anything else that has reserve power? Butting my head against the wall on this one...

 

[Ian Gross]

If the truck is running are you getting 14 volts from the alternator It maybe that your not charging the battery or that it is but not at the correct voltage. Might want to check there.

 

[Travis Munday]

I won't be able to do any running tests until the next few days, until I put the bed back on.

 

[Travis Munday]

Maybe a year old, replaced the original one when it went south.

 

[Todd Z]

Place a test light between the negative cable and the battery terminal( yes disconnect the battery neg cable first)...



Close all doors and turn off everything you think you can...



IF the light is out, there is no draw, if the light is on, then you can start pulling fuses until you find the circuit that is causing the draw.....



Normally door pins, trunk lights, hood lights, stereo amps and Bad diodes in the alternator are the first things I check..



Todd Z

 

[Tom Schindler]

Use a multimeter on the amperage setting. Disconnect the negative battery cable. Connect one side of the multi-meter lead to the battery and the other to the cable. Write down the amperage. Pull one fuse and write that number down then check the amperage. Replace fuse. Repeat with every fuse in the dash. Once you have those done, do the fuses under the hood. If you see little to no change with each fuse removed, I would be willing to bet one of your battery cables are bad. Sometimes a battery cable will corrode to the point where the voltage will creep (I know I am using the wrong term, but you know what I am talking about) around the cable to a ground.



Hopefully Q has some better ideas. He is the most informative and helpful person here.





Tom

 

[Kevin Palmer]

From your explanation I don't think it is your battery based on the fact that it stays charged if you disconnect it.



I do a test similar to what Todd suggested. I use a Digital Volt Ohm Meter and put it between the positive cable and the positive battery terminal.



Open the drivers door and then close the latch on the drivers door, this will let the vehicle think the door is closed.



You will have some sort of a reading on the DVOM. Pull one fuse at a time. Small drops are normal as many items use Milli-amps, (like the clock and memory of the radio for example).



If you suddenly get a large drop or it goes to zero you have found the circuit. This will at least let you narrow down your search.



One thing to do is to do this test and remove the wire from the alternator, if it drops to zero then you have bad diodes in the alternator. Which means, the alternator will charge perfectly but will allow the battery to drain backwards thru the alternator when the vehicle is not running.



Good luck....

 

[Kevin Palmer]

After I posted my message I did a search, this will help you better understand. I still use the DVOM over a light as you get an accurate idea. The light works fine, and will dim or go out if you get the circuit. But,,, it may go out before that even if you get a few of the milli-amp circuits as their will not be enough power to illuminate the lamp.

 

[Ed Barlow]

Any extras like driving or fogliights? I had a similiar problem and it was the foglight switch.

 

[Richard L]

Tiger,

Todd, idea is a good quickie test, and Coastiejoe's is more refined, except that those milli-amps here and milli-amps there will add up and can add up to a more significant drain.



If you follow up with Caymen's advise on the battery cables that should cover the battery cables and all the possiblities except for the battery.



The real problem may still be your battery. The only way to test a battery is to test it under load. Your battery may hold a charge when disconnected, but even a small drain like the clock/radio can be sucking more power than it can tolerate.



My first step would be to take the battery to an autoparts store that does free battery testing and have it load-tested. If it check's out OK, then start looking for an electrical drain.



I have had batteries fail in less than 10 months, so a one year old battery is no guarantee that it's good. even showing 12+ volts does not mean it can tollerate a small drain. Only load-testing can do that.



good luck



...Rich

 

[Travis Munday]

Ebarlow-

I've got several accessories, but I've pulled the fuse for them (one fuse from the battery feeding a terminal block, then all accessories [and switches] feed from that) and the problem is still around.



Richard-

Yeah, I'm taking the battery to get tested either tomorrow or the next day.



I'm hoping the cables are not the problem, they are all new, same age as the battery, maybe a year old. I relocated my battery to under the bed, and as such, ran new wires. The positive is big, fat 2/0 or similar, smaller ground cable that is grounded direct to frame there at the battery. The connection under the hood looks good, but I'll check the connection on the battery end, although it didn't stick out to me as being bad right off.