Thread: electrical draw

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what is the best way to find an eletrical draw. The other day i went out to my blazer to fire her up and click click click. now what the #**@ so i pulled the battery and took it to auto zone and had the battery charged and tested and it only had 9 volts left in it. So since the battery was bought january of 06 less almost a year old. I got it warranty replaced. Brought the new one home hooked it up and i could hear my cd changer trying to do something when the key wasnt even in the ignition. So i am getting ahead of myself here. The guy at the counter said to take a test light and clamp onto the pos side of the battery and get the other end to stay in the neg side clamp and if the light comes on when the key is off i have a draw and to start pulling fuses till it goes out and that should tell me what system is on a draw. Is this true. What is the best way to find this draw.??? does anyone know or think the cd changer should do anything when the key is off.

Take the positive, live cable off the battery. Hook the test light between the positive battery post and the disconnected cable. That way, any electrical flow anywhere in the vehicle will light the test light.

see now that makes sense. cause doing it the way that was explained to me it would always stay on right (testlight). so the way you explain it do i still pull fuses to see when it goes out and that will tell me where the current is????

Originally Posted by 383 chev

see now that makes sense. cause doing it the way that was explained to me it would always stay on right (testlight). so the way you explain it do i still pull fuses to see when it goes out and that will tell me where the current is????

Yes, the way he explained it to you, would cause the light to be on as long as the battery had power and the light bulb had a filiment. The light would be the load and regardless of the fuses pulled, the light would be on.

To prove this, remove the battery completely from the car and hook up the light the way he told you to. The light will be on, and there is obviously no draw from the car.

You could hook it between the negative post and negative battery cable or the positive post and positive battery cable, and then as he said, start pulling fuses to find your draw. Either way will work. But simply connecting a light to from the positive post to any ground on the car will cause the light to come on if the negative battery cable is hooked up.

It is also important to note that most stereo systems (at least the ones with clock and/or the ability to store presets) have a wire connected directly to the hot battery bus of the fusebox. This power line keeps those things in memory when the key is turned off. So the bottom line is, if your stereo has those things, then pulling fuses to turn off the light is not going to help you find the sneaky draw unless you disconnect that wire from the fuse box (or where ever that wire is hooked into).

Does this vehicle also have a computer in it?

Dutch

no. no computer. and i understand taht the memory in the radio needs some juice but when i put the negative terminal on the battery pos was already on i get nice lil fireworks. now this i dont understand either if i do the battery wires vise versa neg first then the pos i get less spark off the pos post i need to find this current cause if it sits for more than 2 weeks i will have to charge the battery. radio memory does not need that much juice. or does it? but i was also wondering with the key off i hooked up my terminals i could here my cd changer kicking on and trying to go into play mode even when the deck was off. this should not even happen IMO till i tell it to at the deck. maybe its time to get rid of the frggin stereo. i am a dummy when it comes to stereo electronics especially when stuff like that happens cause i dont know if it is suppose to do that or not.

Sounds like you have the stereo connected to a hot connection, not switched. The small amount of draw to keep the memory alive shouldn't make fireworks.

For testing as mentioned, a test light won't work very well unless you have a very significant current draw to light it up... test lights are generally for testing the presence of voltage. A DMM set to measure current between the positive post and positive cable would be better but not everyone has one.

Maybe related, my brother has a Chevy Tahoe ~2000 that was eating batteries and it turned out to be a short somewhere in the stock radio. After replacing the stereo, problem was solved. I don't know specifically what failed in the stereo and I wasn't involved in tracking it down but I mention it because perhaps this problem is not uncommon. Do you have the stock stereo system in your Blazer?

As Skids72 mentioned, it would probably be easiest to place an ammeter in series between one of the battery posts and the respective battery cable and measure the current draw. Then, while it is still connected go through and remove and re-install each fuse in the fuse box one at a time while noting the change in the current. When you find the biggest drop of current after pulling the fuse, you have more than likely found the power lane your culprit is connected to (depending of course on how much it is actually taking). I say more than likely because I don't know what wiring mods have been made to the vehicle and what all is connected through fuses as they should be and what is simply directly wired.

Good Luck,
Dutch

alright i will see if i can use my bros ammeter. to answer an other question the stereo is all after market sony xplode deck, sony 10 disk cd changer, fosgate (4) 6x9's (2) tweeters 1200 watt amp and 12" sub

you didn't say what yr. car you had. if its got a computer, it will show a draw through the test light also.

Originally Posted by lt1s10

you didn't say what yr. car you had. if its got a computer, it will show a draw through the test light also.

there is no computer in this vehicle it is an d 85 s-10 blazer 2wd
it does have and msd 6 plus box in it though if that helps

I'd be concerned about the stereo and amp connections.

I had the same sort of problem with my 02 dodge pickup, nobody could find the what was causing the battery to go dead. Went through 3 batteries (1 stock and 2 sears dihards) Everything checked out OK. Turned out to be the aftermarket electric brake controller. Now I only connect it to power when I need to tow.

Most digital DVM will let you check for amps to about 10 amp in series with the postive battery lead will give you an amp reading. don"t use any feature that will get you above the 10 amps. VERY COMMON to have an alternator diode go and give a load on the battery would try to disconnedt it and test for amps. I had that one once. #Ed ke6bgnl

Disconnect one of the battery cables, then disconnect the alternator. Connect the battery cabkle back up. If there are no sparks the alternator is shorting out. If that isn't the problem, then try the fuse thing.