1989 GT Battery Draining - what do these numbers indicate? - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 4 Old 03-13-2012, 11:56 AM Thread Starter
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1989 GT Battery Draining - what do these numbers indicate?

Hey guys,

Problem is a 1989 Mustang GT won't start after sitting for 3 or more days.

Battery is brand new.

Battery voltage engine off = 12.6 Volts
Battery voltage engine on = 13.8 to 14.1 Volts

Amperage reading from negative post on battery to frame with negative battery cable removed:

Key off - all circuits off = 0.17 Amps constant
Key off - all circuits off - #8 fuse removed = 0.0 Amps Constant

The fuse diagram is attached. Any thoughts on this? What would you do next?

Phil

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post #2 of 4 Old 03-13-2012, 11:30 PM
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.17 amps is not alot of draw. generally under .4 is considered acceptable. if your measurement is accurate at .17a you must have another intermittent drain or a weak battery to lose charge in just 3 days

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post #3 of 4 Old 03-14-2012, 08:49 AM Thread Starter
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Quote:
Originally Posted by luch90 View Post
.17 amps is not alot of draw. generally under .4 is considered acceptable. if your measurement is accurate at .17a you must have another intermittent drain or a weak battery to lose charge in just 3 days
Good Info.

I think my next step will be to take a daily reading on battery voltage while it sits to see how fast it is draining.

I had a couple of other issues with the car I fixed prior to taking the amperage reading that may have been part of the problem.

Phil
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post #4 of 4 Old 03-14-2012, 01:22 PM
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For me I use a multimeter that has mA setting. First you want to remove negative battery cable. The put the multimeter b/t negative cable and neg terminal on battery. The setting the multimeter should be on first is 10A, unless your multimeter has a lower setting. If you start off with the multimeter in mA you will pop the internal fuse of the multimeter(MM).

Once of 10a setting see what your reading is once setup. This is with key off also BTW. If it shows like 1 or .5 or something like that. Then something is draining it quite a bit.

Start pulling fuses (take note as to where they go) until you all of a sudden see the amps drop. Now change the multimeter to 200 mA or the highest setting for mA. Check and see what it is, it should be lower than 100mA on most cars. Depending on options and accessories your car came with. A manual should tell you what the key off draw should be.

Anyways once you found the problem, look up the circuit wiring diagram and see what all it powers. Usually it's a radio or door switch that give the most issues.
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