[DeTomaso] Why Is My Battery Discharging?

John Donahue demongusta at me.com
Wed Dec 17 19:46:53 EST 2014


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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