[DeTomaso] Why Is My Battery Discharging?

[Larry - Ohio Time]

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