[DeTomaso] Why Is My Battery Discharging?

Ed Mendez edducati at mac.com
Wed Dec 17 21:08:49 EST 2014 

Do you have a battery disconnect? Still discharging?

Battery?

If not this is something energized pulling a current.

.02 cents

Sent from iPhone 5s

> On Dec 17, 2014, at 16:46, John Donahue <demongusta at me.com> wrote:
> 
> Been following this discussion, and could not resist to comment on the first sentence  - 5th paragraph (I think) - since I am a veterinarian (DVM) - and have been known to be "sensitive". LOL
>> On Dec 14, 2014, at 5:05 PM, Larry - Ohio Time <Larry at ohiotimecorp.com> wrote:
>> 
>> 
>> 
>> Hi Ed,
>> 
>> Lots of very good advice, but I do things just a bit differently (that
>> should not be surprising). 
>> 
>> I have an old "trouble light" that I have modified. Cut the 110vac end off
>> and install two larger alligator type clips on the wire ends. Now change the
>> light bulb to a 12 volt model. You can find them at RV stores.
>> 
>> Now hook this between the battery post and the removed battery cable, like
>> the others have said. If there is a load (drain) the 12 lamp will light up.
>> Now take this light to the fuse box as others have told you to do. When the
>> light goes out you found the problem. You can get good at determining the
>> amp draw by how bright the lamp is after a wile.
>> 
>> You are going to need a light anyway :)
>> 
>> The problem with a DVM measuring voltage is that they are very sensitive. I
>> have measured voltage from the positive post to the top of a dirty battery
>> case. 
>> 
>> An Amp meter is the way to go but they can be costly (I have two Sun units
>> for sale) and then you need to crawl out from under the dash, walk to the
>> battery and bend over to read it. That takes me about 20 minutes each time.
>> 
>> Thinks to remember:
>> 
>> If you open a trunk, hood, door, glove box and a light normally comes on
>> this will look like a drain (short) when you open them during testing.
>> 
>> The battery is draining when the car if off and key is out, so look at the
>> things that work then, horn, lights ect.
>> 
>> You do not want to kill your new battery so do not leave it hooked up until
>> you find the problem. It can also be a fire safety problem should the drain
>> turn into a short.
>> 
>> In Pantera's I have found bad horn relays, voltage regulator and I think a
>> back up switch on the ZF that have done this.
>> 
>> Larry (sparks) - Cleveland
>> 
>> 
>> -----Original Message-----
>> From: DeTomaso [mailto:detomaso-bounces at poca.com] On Behalf Of SOBill via
>> DeTomaso
>> Sent: Saturday, December 13, 2014 7:24 PM
>> To: detomaso at poca.com
>> Subject: [DeTomaso] Why Is My Battery Discharging?
>> 
>> 
>> Ed,
>> 
>> At http://www.panteraplace.com/Electrical/Power%20Distribution.pdf you  
>> will find a diagram showing the electrical power distribution on the
>> Pantera. 
>> This diagram is the Big Picture based on a stock Pantera electrical  system 
>> and was made at the suggestion of and with the help of Lee Farrell.
>> 
>> How to find out why a battery is discharging?
>> 
>> Disconnect the negative battery cable. Now the battery can not be  
>> discharging into any circuit in the car. Measure the battery voltage with a
>> 
>> multimeter which can read to at least 0.01 volts. Such meters are readily  
>> available and are quite inexpensive. If your battery voltage is slowly
>> decreasing, 
>> the battery is being discharged. What does "slowly deceasing"  mean? My 
>> battery voltage did not vary by +/- 0.01 volts measured over 5 minutes.  If
>> your 
>> battery voltage is slowly decreasing when the battery is not connected  to 
>> any load, you have a bad battery.
>> 
>> If the battery is good, why is it discharging?
>> 
>> Reconnect the negative battery cable to the battery. Measure the battery  
>> voltage. If the battery voltage is decreasing, the battery is  discharging 
>> thru a load in the car. Looking at the Power Distribution  Diagram. How can 
>> the battery discharge? The battery could discharge thru the  Alternator, the
>> 
>> Ignition Switch, the Headlamp Switch, or Fuses 7,8, or 9. Since  the
>> Headlamp 
>> Switch is OFF, and the Ignition Switch is OFF, the battery could  only 
>> discharge thru the Alternator or Fuses 7, 8, or 9. Since the fuses are  
>> relatively easy to get too, pull Fuse 7, If the battery voltage continues to
>> drop, 
>> replace Fuse 7 and pull Fuse 8. If the Battery voltage continues to drop,  
>> replace Fuse 8 and pull Fuse 9. If the battery voltage continues to drop,  
>> replace Fuse 9. Unless there is more than one problem, we have eliminated
>> the  
>> circuits associated with Fuses 7, 8, 9 as the source of the problem. On the 
>> assumption that we have a single circuit causing the problem, I recommend  
>> pulling and replacing fuses one at a time. It is no fun to wind up with a 
>> pile  of poorly marked fuses to sort out against a diagram. A more
>> scientific 
>> approach, which accommodates multiple causes for the problem, is to pull a 
>> fuse,  mark it as to location, and do not replace the fuse until we have  
>> solved the problem. Do it which ever way makes the most sense to you.
>> 
>> The next item to test would be the Alternator, but, since fuses are easy  
>> to access, pull fuses one at a time and recheck the battery voltage.  If you
>> 
>> pull a fuse and the battery voltage stops dropping, you have found  the 
>> circuit that is draining the battery. If you have tested all the fuse
>> circuits 
>> and the battery voltage is still dropping, the only component left is  the 
>> alternator.
>> 
>> To this point, we have had life fairly easy and we should be done is less  
>> than one hour. Life, unfortunately, is going to get a little less easy. We 
>> must  get to the Alternator.
>> 
>> How to find out if the drain is in the Alternator?
>> 
>> Disconnect the negative battery cable from the battery. At the rear of the  
>> Alternator remove the Big Black wire and be sure it does not touch the 
>> chassis.  Reconnect the battery negative cable to the battery. If the
>> battery  
>> voltage continues to drop, the problem is not in the alternator. If the  
>> battery voltage stops dropping, the diode pack in the alternator is the most
>> 
>> likely problem. Any auto electric shop can easily fix this problem.  
>> Disconnect the negative battery cable. Reconnect the big black wire at the  
>> alternator. Reconnect the battery negative cable to the battery.
>> 
>> If you have done all of these tests and the battery voltage still continues 
>> to drop, something quite strange is happening IF YOUR CAR IS STOCK. If 
>> your is  not stock, disconnect whatever is not stock and see what happens.
>> 
>> This all sounds quite complicated, but it really is not. Look at the  
>> diagram, think of what you eliminate when you pull a fuse. There is no
>> magic: No  
>> Fuse = No Drain. The problem can be found.  Let me know what you find in  
>> any case.
>> 
>> SOBill
>> 
>> The main  thing is to keep the main thing the main thing.
>> Do the best you can with what  your have where you are.
>> Have fun today!
>> SOBill  
>> 
>> 
>> 
>> 
>> 
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