Why is my battery draining....???

P

PhilKendell

New Member
Can anybody help me find out why my battery is draining down whilst the vehicle is not being used?
I have a 1974 3500 V8 auto and when I go to my car after it has not been used for a week or so the battery is completely flat. I purchased the battery in Sept '02 and all seemed fine up until about 6 months ago. If I charge it overnight it's fine and starts first time when re-connected
The interior light(s) switches off with all doors closed, as does the light in the boot (I climbed in and checked whilst someone closed the bootlid) and all other side/headlamps are off so I am at a loss as to what could be causing it. I've fitted an old period Motorola radio but that only works with the ignition switched on.
I'm no auto electrician so answers of one syllable and not too technical would be appreciated.
Thanks.......Phil.
 
hi phil
dissconnect the battery earth lead at the clamp and put a test lamp between the earth lead and battery post.with everything turned off the test lamp should not be illuminated.
if it is illuminated you will have to start by removing the fuses one at a time and see if the test lamp goes out.if removing any of the fuses puts the test lamp out you will need to trace and isolate the item the fuses is related to.
if the lamp is still on after removing all of the fuses i would recomend that you disconect the altenator and see if that puts the test lamp out.they have been known to drain the battery if it goes faulty. if the test lamp is not lit you will need to have the battery leak tested because it may still be a duff battery
above all else take great care not to short out the wiring
nick
 
Hello from Australia,

Had similar problem with my 3500. Turns out that there is a permanent but very small current feeding to the alternator. (exciter field maybe?). Obviously, after a period of idleness, the battery will lose its charge, but it would take several weeks to do it if the battery is in good nick. Also , the clock is on all the time too. I had the dash out and wiring disconnected all over the place before realising the problem. The battery was faulty too, which did not help the diagnosing. The battery was relatively new so was not a suspect, replaced under warranty.
 
The current drain from the clock and the very small leakage accross the diodes in the alternator should not add up to more than a few milliamps and after 4 months stood my P6 still has enough power to start. It sounds as though you have a more serious leakage and I would check the main battery joint under the carpet on the right hand side under the drivers left foot. If the carpet is damp I have known them to grow verdigree and cause leakage current, otherwise I would suspect a faulty diode in the alternator.
 
I had a similar problem many years ago with a 2000. Battery going flat yet everthing appearing ok. I finally traced it to the wiring loom having chafed through. A bundle of wiring goes from back to front along the inside of the car under the carpet by the sill. This then goes through a hole in a panel under the A post. There is a grommet but in this case the wiring had worn through the insulation and was shorting occasionally. A bit dodgy as it could have caused a fire, I suppose. Worth a look, or it could be a worn bit of insulation anywhere, just to cheer you up!
 
You must log in or register to reply here.
Back
Top