QuestionI have a 1987 Dodge 600. Recently replaced both the battery and the alternator but the battery still loses its charge. Any suggestions on what could be causing the problem?
AnswerHi Sylvia,
Another person with a Dodge (1991) wrote to me with a similar problem last year but it was a little trickier because it wouldn't discharge the battery all the time, only intermittantly. But the principle of how to find the problem is identical:
"I suspect there is an intermittant short circuit or battery draining component (for example the trunk light sometimes being "on" which you wouldn't recognize, but the switch which turns it on is just on the edge of being "on" when it shouldn't be). The best thing to do is get yourself a volt-ohm-milliamp meter from an electronic supply store. It should be in the range of $20. Then you can simply disconnect the - post of the battery and put the leads of the meter between the post and the disconnected cable and read the current flowing. Then start removing the fuses one at a time to see which fuse, when removed causes the current to drop to that vary low value that was measured by the mechanic. Then note the purpose of the fuse and we can take it from there. I have the wiring diagrams for the '91 and I can tell you which items specifically are on that fuse and we can remove them one at a time till we find the one that causes the current to drop when the fuse is of course in its position. If you can't find a milliamp meter at a modest price, and rather a meter that only read volts and ohms, then there is another way to do the measurement. I gave this answer a few months ago to another lady who had the same problem: "On the battery draining, there is something that is draining the current even though you don't know anything as being turned on. The best way to find what is causing the draining is to obtain a volt-ohm meter at an electronics store or an auto parts store, or borrow one from a friend. You should be able to get one for under $20. Then you disconnect the clamp from the "-" or "neg" post of the battery, then remove the "+" or "pos" clamp. Then put the two test leads of the meter on the two clamps (one lead on each clamp) with the meter set to read ohms. It should read something less than infinite, but you would like it to read more than 1,000 ohms and ideally much more ohms than that, which would mean there was no source draining away the charge. If instead you find that it reads only 5 or 10 ohms that means there is a component that is draining the battery.
The procedure to find out the drain source is to disconnect each of the fuses that are assigned to a specific circuit in the car, one at a time, and see if the meter reading moves toward infinity as the result. If there is no change in the reading of the meter, then replace the fuse and move to the next one in the fuse box and see if it causes an increased reading, etc. When you find one (or more) such fuses that when removed caused the reading of the meter to go up significantly, then look for the label on the fuse box for that fuse, put the fuse back so that the reading decreases again and begin to unplug each of the electrical items that are powered by that fuse and keep checking until you find the item that causes the reading to go up again. That is the faulty component that is causing your problem.
You will want to do these tests with all the doors closed so that no lights are "on" and the car is sitting just as it is when you have it shut down. Be careful not to change anything about the car doors/lights (always close the doors before reading the meter) while you are doing this testing or none of it will make any sense.
You will find the fuse box under the dash in the passenger compartment on the driver's side of the car close to the side panel. The label(s) on the fuses in the box under the dash are the relevant search clues. This is something you can do yourself and save labor costs by so doing. If you find a fuse that when removed causes the reading to rise significantly, tell what the number of that fuse is and I will tell you what to do then to solve that problem specifically (how to unplug the suspected faulty item).
Whenever you go to reconnect the battery, always put the + post clamp back on first, then put on the - post clamp. The reverse is true when you disconnect the battery (as I described to you at the start). It is done that way for safety so you don't accidentally short the battery and get a burn."
So the concept is the same whether you do it by measuring the milliamps with the battery in the circuit or the ohms with the battery out of the circuit. It is a bit more reliable to measure the milliamps because some electronic components will function differently depending upon whether they have a battery voltage applied to them or not. And it is a little safer to just deal with the - post and not both battery posts as far as accidentally shorting the battery to ground with a tool on the + post (if you have forgotten to remove the - post first or to put it on the battery last).
I also think that you would do well, since this is happening so regularly, to preventively do a measurement at the time when you are going to leave the car for overnight or if that is too often maybe for a few days, and then you might catch the gremlin before the battery discharges. Even if you can't take the time then to fix it, at least you can come back when you need the car and the battery will not be discharged. Of course, you could just disconnect the battery all the time, but then that wouldn't solve the problem and get very tiresome, too.
So let me know if you go this route and also if you have any questions. It being intermittant is what is going to make it expensive and frustrating to have a shop try to find the cause. But you can find it yourself, maybe even without my help. But I'm here to give you advice."
Let me know what you find out or if this isn't clear.
Roland
