Hi guys!
I've driven my car everyday for a couple years now & have had no problem.
Over thanksgiving I was gone for a week & I came home to a "completely dead",battery.Not even a click.
So after experimenting I find that after 2 days sitting the battery is weak but starts the engine ,After 3 days sitting,It will crank but not long enough to start.
So this is what I thought would work but didnt.
I hooked the OHM meter between the battery post & the disconnected positive battery cable,& It read 12.28 volts,then I removed every fuze one at a time.I did it also on the negative side of the battery with the same results, = none.
The cold weather isnt helping but its a 2 year old Diehard gold battery.
How can I figure out what is drawing the current?
Your help is much appreciated.
In the mean time I'll just drive it everyday.Ha
Its an all stock 84 auto.

 

I won't be much help to you, but I had the same problem and ended up replacing the battery and problem never returned.

 

You need to use a DMM with an Amp scale; connect it between either side of the battery and the disconnected wire and take a reading of the leakage current. Start with the highest scale and go lower if necessary.

Then pull each fuse in turn until the reading drops substantially. Once you find the offending circuit you can proceed to isolate the short.

 

Just a quick reminder. Unless you have a high-end DVM or a specific Ammeter, the most DVMs can usually only handle a load of 200mA running through them. A 1 amp draw will take your batter down after a day (did in my case) so I would say if you have a load taking it down, it is appreaching 1/4 to a 1/3 of an amp (250mV to 333mV). You might blow the fuse in the meter checking this. If possible, find a buddy with an inductive style ammeter. -Matt-

 

Hey thanks guys,I knew ya hooked the meter up as stated but I was wrong on which scale to use.I was useing Volts & thanks to you I will try Amps.
I am using a good Digital muti meter.I'll have to check the instructions on fuze size in the meter.
Now tell me this, could I pull a fuse then hook the ohms scale to the fuse socket, load side, & ground the other meter lead and check each circuit that way?
Thanks again to all.

 

No, no, no, no, forget OHMs, that measures resistance only and will hurt your meter if any voltage hit it.

You can (with battery reconnected) pull a fuse and use the same AMPs (current) scale to measure across the fuse terminal. This will tell you the current passing through each fuse.

Don't forget that there are also connections to the battery through the block below the battery that don't go through the fuse block (but have their own fusable links built into the wires).

Also depending upon your meter, their may be diffent sockets to plugs the leads into to measure current (amps). Capacity may be marked on the case near the plug socket; i.e. 100 mA or 10A. Always start on the highest scale first (i.e. 10A) and move down carefully. **** on meter may have to be selected based upon current / socket necessary.

Pete

 

First let me say that it is obvious but forgotten that when you are checking things on your fuse panel, your interior lights are on. Either pull the CTSY fuse or put tape over the door jamb switch to keep from getting false readings.

The next thing is, your multimeter will have a scale on the front. Whether it is a dial or push buttons, it will have the maximum amperage that it can handle on a corresponding location. If you don't have this, then it might be an automatic ranging meter and the rating will likely be on the back of it.

Readings for volts and ohms are generally done using the same lead connectors to the meter. Readings for amps generally uses a different receptical for one of the leads. The way a RMS meter works allows it to read a very high voltage, but the setup usually leads to a lackluster capability for reading amps (manufacturers usually skimp on this scale).

In a perfect world, you would be able to disconnect the negative battery cable and connect the meter, set on Amps and using the correct recepticals, in line--meaning it is in series. If there was no short, the meter would read trace amperage (1~10mA) for stuff like the ECM and the radio memory. The problem is that 200mA may or may not use the battery up over 2 nights.

If you want to use the fuse block method that you mentioned, you MUST disconnect the battery. Put your meter on OHMS, clamp one test lead to ground, and WITH THE BATTERY DISCONNECTED probe the side of the fuse terminal that is NOT normally hot. If you get continuity (i.e. 0.000-0.004 on your scale) then that circuit is causing the direct short. If it was this easy though, the fuse would blow because there is a direct short. When using this method, you are reading the resistance of various solenoids, injectors, bulbs, etc that are on the circuit and you really wouldn't know which resistance you would be looking for.

The other idea I have is to use an old brake light bulb and socket. Disconnect the negative battery cable and put one wire on the negative cable and one on the negative post. If the bulb blows right away, then you have a healthy short. If the bulb glows brightly, start pulling fuses and when the bulb get a lot dimmer, you have found the problematic circuit. The bulb method might also be useful when you have a 400mA load and your meter can only read 200mA. The added resistance *should* be able to bring the load down, but I have not verified this on my Corvette...just my old 69 Chevelle that didn't require constant power to a clock, radio, or ECM.

If all else fails, see what forum member jfb has to say. He knows his electrical. Good luck, -Matt-

 

JHC, did I **** off HighHopes85 also this week? I like JFfriggenB also, he is a smart guy. Just so you know I've been in the communications / electronics industry for over 25 years Master HighHopes85, and I have meters older than you.

The proceedure I described above is accurate, if not detailed. Why are you "dwelling" on OHMS for gosh sake? Forget resistance, forget bulbs, the man has a meter. If it can read current at any level the best way in the world is to start by reducing probable sources of the drain. BYW, I believe my ECM is about 30 mA, not sure about the radio (but the 30 mA may include the radio and VATS).

I would start at the battery. Pull the negitive cable and put the black lead on the battery neg terminal. Put the red lead on the negitive battery cable connector. Black lead should be plugged into the common plug on the meter (if available), red lead should be plugged into the highest current plug on the meter (in order for example, highest to lowest: 10A, 1A, 500 mA, 250 mA, 100 mA). If the meter has no current input higher than 100 mA I would not use it for this test.

If battery draw proves higher than about 30 mA, then reconnect battery cable and move to fuse panel. Forget interior lights for now, it will not effect any fuse but that fuse that also has the interior lights on it. Pull each fuse in order and place the leads (meter also in AMP - same as battery), you should try and find the fuse (s) that add up to the total draw you read on the battery. If the draw you read across the (empty holders) fuses does not equal what you read from the battery then you need to check the fusable links below the battery. If one fuse draws a lot of current (and it's not the interior lights) continue to trace that line. A shop manual and wiring diagram is a good resource here.

Also check the alternator for current draw (this will be one of the fusable links, however you could quickly pull the main wire on the back of the alternator and use your meter in the same way to make sure it is not drawing current from the battery - hense shorted). Alternators can have a problem that will drag down the battery.

Pete

 

Holy Cow...WTF are you talking about?!?!? Just so you know, your post right before my last one wasn't up when I hit reply and my reply had nothing to do with yours at all--BECAUSE I hadn't even seen it!

The original poster stated that he ran his meter in series with the negative cable. He then stated that this gave him a voltage. I saw a problem with this, as I am sure others would have and realized that maybe he was either (1) Confused on how to use a meter correctly or (2) Wrote down his procedure wrong. Look, it ain't my meter so I could have just told him to carry on and blow his up, hoping that the fuse would protect it, but would that have been morally correct? Nah.

I worked auto parts for quite a while. Within the first 10 seconds of meeting a person and listening to their problem, I had already figured out which language I would be using with them and which angle I would suggest that they tackle the problem from. No two people are the same and generally, the customer was more satisfied if I played on their level instead of trying to blow them out of the water like I could have.

You can find a short at least 10 different ways. The light bulb in line with the battery cable is one of the easiest and quickest ways to do it assuming that you have a spare socket. I would rather burn up a lightbulb than a meter. Again, I was using the fact that it was stated that the meter was incorrectly hooked up before and this was a quick and easy test that would at worst, burn out a 75 cent bulb.

He asked if he could use the resistance readings. Since he asked, I told him how he could. Again, if someone asks a yes or no question, they probably want an answer to their question.

I checked the current drain on my car with ECM, aftermarket radio, etc and you are correct. My current was 0.05A so my earlier post was jaded stating only 0.00-0.03A.

That is EXACTLY what I was geting at! Why were you hounding me for it??? Gee whiz!!!

If he left the CTSY fuse plugged in and then checked voltage from ground to ground, he would show trace voltage. This threw me for a loop and made it seem like I had a live ground which I did not. I am sure that with 25 years of experience you would have caught on to this right away but I did not. I didn't want him to pull his hair out trying this arrangement.

Pete, I respect your post very much and have no arguments about the way you mentioned testing things. But how the hell did I step on your toes with what I said? :confused: -Matt-

 

Ok guys,no arguing .Ive done that before where 2 people are entering answers at the same time & it ends up not making alot of sence,but actually it has help by adding more detailed info.
So thanks everyone.
I will try the amps across the fuse blocks & may try the bulb at the battery meathod if nessesary.
I kinda suspect the light that lights up the shift indicator in the consol as that light doesnt work,but it could just be a bulb.
I will post my results tonight.
I really appreciate all the help.
:chevy

 

Thanks again for the help guys.
I checked my DMM & found its highest scale is 200 mili amp.So its worthless for this application.
I guess I'll try the light bulb across the fuses method monday .
Thanks again.

 

I didn't read every word written above, so if this repeats advice already given, my sincere appologies.

Years ago I did the exact same thing with my MG. After a couple of days the car wouldn't start; I convinced myself that there was a current draw, so I spent weeks chasing a short circuit that didn't exist.

With batteries it is always the basics. Enough water in the battery, battery cables clean, tight and corrosion free on both ends. Sufficient charge on the battery after the car starts.

Unless someone has chopped up your wiring harness, I wouldn't suspect a short circuit.

Good Luck. I am curious how this turns out.

 

I had this problem last summer. Looks kind of silly carrying around jumper cables in the back of a Vette.

Anyway, I did the meter thing with the Amp portion of my meter and watched the needle head off the charts the first time I hooked it up. Yup, too much current for my meter, luckly it was fused.

So then I hooked up a 12V light-bulb between the battery and the negative with everything turned off and the bulb lit. I wasn't out of the woods yet becuase of the draw from things like the hood lights and the doors (like people have noted). So I unpluged that fuse and then I determined that there was another fuse (other than the problem circuit) that was drawing power. I think it was the ECM fuse. I think it stores your gas milage information and such when the car it off. This means that I had to take out two fuses and assume that the problem was not within those circuits.

Good news for me, because the light was still on. It turned out to be the either a door lock or power seat problem. Disconnecting them one connector at a time, I found the problem in the driver's seat motor. I disconnected it and that is where it has been ever since. One day I'll get in there to fix the problem, but it is low on my list since it doesn't drain the battery anymore!

Jim

 

nobodyunknown, you can get a very nice DMM at Radio Shack for around $50 which woulc be useful later on with your Vette.

Also, you can make a test light from a mini LED in series with a 1k Ohm resister and a copla aligator (roach) clips.

Good luck.

 

I made a test light out of a brake light bulb,pulled each fuse one at a time & hooked the test light accross each fuse holder. the only one lighting the bulb is the curtesy, clock fuse.
Remembering what I learned here I pushed the door jam button.Light stayed on .I thoght I'd found it tell now I remember theres 2 buttons I need to push.The one thats at the back of the door opening.I think its for the door ajar light but Im not sure.
If it is that circuit It could be anything from interior lights to radio to alarm to horn.......
So let me check alittle further & get back to you all. When I do figure it out I will let everyone know .
Thanks again Greg

 

this is a good topic i have the same dayum thing my battery keeps gettin drained :D

 

I have the same problem with my 84. Installed a new battery and the same thing, leave it sit for 3 days and the battery is dead. Keep us posted!
Thanks,
Dave

 

Since you know that the only 2 fused circuits on the fuse panel that are carrying current are the CTSY and radio/ECM fuses, pull those and then hook the bulb inline with the negative battery cable. There are constant +12 circuits only protected by fusible links. The fuse panel doesn't receive these circuits so if the bulb stays lit with the 2 fuses pulled, then you know it is on a circuit protected only by a fusible link. Don't forget to pull circuit breakers on the fuse panel when you do this. -Matt-

 

If you want to use your DMM that only goes to 200 ma., then buy a 1 ohm 10 watt (or higher power) resistor and use your DMM to measure the volts across the 1 ohm resistor when it is in series with the circuit you are trying to measure the current in. Your voltmeter will now read directly in amps. If your voltmeter reads 0.1 volts, then 100 ma (0.1 amp) is flowing through the resistor. The 10 watt resistor can only safely carry 3.3 amps for long periods, and it will get hot at this current level. Now you can start your voltmeter off at 12 volts or higher full scale and then turn its full scale reading down (lower volts) to see what the leakage current is. You can do this on each fuse clip (fuse removed) and learn what the leakage current is for each circuit. Unfortunately there are about 8 fusible links in C4's and most are under the battery jump start terminal and they must be disconnected to get an ammeter in series with them. Here is one place a clamp on DC ammeter is very useful.

 

Its deffinatly the crtsy fuse.
I got the bulb hooked between the neg.post & wire.Its pretty bright , I guess I'd desgribe it as half bright cause if I turn something on it gets brighter.
But that fuse works so many things I dont know where to start.
Im working on it right now,gonna study the wiring diagram & try to think if any of those things are not working.