NEED HELP, electrical problem with my car, Key off,power runs from battery

but it passes the test for charging..only drains the battery dead whin the key is off, it measures 12 volts from the battery post to the cable that is going down to the Alternator..that wire leads to the problem, the one that bolts on to the alternator, detach it and the voltage drain stops, i have replaced 3 alternaters, last one i had checked off the shelf at the store, before i put it on and it was bad too.. and this has also ruined a battery, I cant afford to take it to a shop..

it is a simple 1987 Nisson Sentra...

any mechanics out there..???

if he knows when he gets in but in the meantime try the auto board someone there might have a clue

http://www.democraticunderground.com/discuss/duboard.php?az=show_topics&forum=310

You can't test for erronous draw with a voltmeter--you will always get 12 volts. The way to do that is connect a test light between the battery post and the cable. Use the negative side for safety--then start pulling fuses until the light goes out. Check for obvious stuff staying on first, glove box light, trunk light, cigarette lighter pushed in. Remember to keep the doors closed or pull the bulbs from all the interior lights; and don't forget to the engine compartment light if there is one.

There is always some draw, usually around 200ma and that's the normal current for radio memory, alarm systems, etc. Including the wild goose you're chasing, normal leakage through the alternator diodes.

The important thing is to look for excessive current, not voltage. You can use an ammeter, but unless you have a baseline the numbers won't help much. That's why I like a conventional test light because the nominal draw will generally not be enough to light the bulb.

Hope that helps!!

battery.. It ruined a fairly new battery 750amp battery... i dont have an amp guage, but will solder up a tail lite bulb to test with..

thanks, i didnt know there was a constant draw thru the diodes.. but the last 3 anlternaters drain the battery overnite... by the time the problem ruined the battery.

not saying it can't happen--I've seen weirder shit--but I'd put my money on something else.

You may find a taillight bulb needs too much current to to give an accurate test; a dash light bulb or interior light might work better.

side, this alternater only made it glow red for about 1/8 th inch on the top of the filament. it make no color on a brake lite,

check the positive cables, might be worn in spots and grounding out.

and are the alternators rebuilt or new?

are generally poor quality unless they come from the dealer, and even then, I've had some problems.

thinking too.

Have you tested the battery? If it has an internal short or a "dead" cell it will self-discharge. The easiest way to test for that is leave the battery disconnected overnight and see if it will start the car in the morning.

On Edit: Be safe! Batteries--especially ones that are not in perfect condition--can literally explode. Eye protection (I like a full face shield) and gloves will keep you out of the emergency room.

It was the CD player. If it wasn't manually turned off when the car was turned off, it would drain the battery.

Good luck!

Other possible causes:
Engine cooling fan if it is designed to run for a cool-down period after engine-off.
Any system that keeps lights on after you leave the vehicle.
Horns -- they can stop making noise, but still be stuck on.
Power door locks; moisture or corrosion can cause partial shorts.
Same for power seats and mirrors.
Power antenna if it is designed to retract at key off.
EFI/engine control computer.
In short (no pun intended) anything that works with the key off can potentially cause a problem.