1989 Mustang battery is draining

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  #1  
Old 08-11-04, 09:39 PM
HorseWithNoName
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1989 Mustang battery is draining

In the past month, I've had the problem of a dead battery if I don't drive the car for several days. If I drive it at least every other day, it starts just fine. I don't usually do my own car repairs but I'm somewhat mechanically inclined, so if it could be something simple, I would like to take care of it myself before I pay the dealership $200 to change a fuse .

If anybody has any ideas, I would love to hear them. In the meantime, I'll be driving my car at least every other day.
 
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  #2  
Old 08-11-04, 10:11 PM
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You could have a "iffy" battery that can't hold a charge, or a short somewhere slowly draining it
How old is the battery?
Also: is it a 4 cyl. or 8? And do you have a voltmeter?
 
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Old 08-12-04, 10:53 AM
HorseWithNoName
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I replaced the battery (with an Energizer 58-610) myself in early December 2003 and didn't have any problems until this month. I was also thinking along the lines of a short somewhere and was hoping I could find it and fix it myself, but I don't know how complex that would be.

The car is an 8-cyl and I don't currently have a voltmeter.
 
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Old 08-12-04, 11:37 AM
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A cheap analog volt meter would be a big help. One no cost thing you could try is to remove the bulbs - if you have them - from the under the hood light, glove box light, and trunk light. If one of those switches is bad, the light could burn constantly with out your knowledge and drain the battery over several days.
 
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Old 08-12-04, 12:29 PM
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Removing the bulbs will do no good if the module that controls them is still energized. You need to find out if you have a draw, and if so locate it. Start out by testing for a draw. You can do this by removing one of the battery cables and installing either a regular test light or ammeter in series between the cable end and the battery. First disable the door jam switch so you can access the fuse box without activating the interior lights. Next take a jumper wire and also put it in series with the meter or testlight, whichever you are using. This is to expire all the timers. After a few minutes remove the wire and see if the light is on or the meter reads over 50mv. If it does, that means you have a draw. Now start removing fuses, one at a time until the light goes out or the meter comes down. When this happens, you have found the right circuit. Now see what operates on this fuse and narrow it down to the component doing the drawing. If you find you don't have any draw, try leaving the battery disconnected overnight and see if it still loses it's charge. You could have a bad battery.
 
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Old 08-12-04, 01:55 PM
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Live and learn. I didn't realize that the three bulbs I mentioned were controlled by modules/timers. I thought that they were wired thru a fuse to an always hot circuit directly. I didn't get into the current draw because HorseWithNoName said he did not have a meter. Maybe he does have a test light.
 
  #7  
Old 08-12-04, 03:29 PM
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Most interior lights these days have a delayed off which takes a module to control that. Modules are also in the circuit to warn about keys left in, lights left on etc.
 
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Old 08-12-04, 03:44 PM
HorseWithNoName
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That sounds like something I can do! I would imagine a testlight or ammeter would be fairly inexpensive.

On a related note, I seem to remember reading somewhere that deep cycling on batteries can damage them. Is there something I can do to this battery (if I find it is any good after following the previous instructions) to repair that damage?

I really appreciate all of the responses. I already feel great about at least trying something before taking it to the dealership. Thanks everyone. I'll let you know how it works out.
 
  #9  
Old 08-12-04, 06:57 PM
chadtoolio
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Don't be tricked by modules that are creating a draw, but when power is removed(taking cable loose and putting meter in line) the module that is creating the problem also stops drawing current. One way to eliminate that problem is to never break the circuit. Put one lead of the Ampmeter on a good chassis ground, then connect the other end the the battery negative post/cable end. Then disconnect the negative battery cable where it is connected to the Chassis/engine etc... The ampmeter is now the completed circuit and you never created and open circuit situation. Proceed with finding the draw like suggested in earlier posts(removing fuses,etc..) Test lights are no good for these tests. The right way is to know the maximum current draw and check for that, but you obviously have much more than that. With that said, as suggested earlier, use a ampmeter/dvom that has a MA scale. You shouldn't be drawing more than 50MA.

Chad
 
  #10  
Old 08-13-04, 11:13 AM
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Does the vehicle have an alarm? I've seen some alarms, that when had problems, drain the battery. Resetting the alarm sometimes takes care of this.
 
  #11  
Old 08-13-04, 01:36 PM
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Do it the way I said and you'll be fine. A normal test light WILL be sufficient to determine if you have a big enough draw to be a problem. If the bulb illuminates at normal brilliance, you have more than 50ma. Breaking the circuit and reconnecting it is what will activate some modules, especially alarm modules. That's why you allow sufficient time time expire them. That's another reason to break the circuit first so as to see what the expiration time is. If the vehicle is equipped with an alarm and someone disconnected the siren, the system will continue to draw silently.
 
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