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Easy Way to find an electrical short that drains battery?

I have a 93 911 Cabriolet and have a electrical short somewhere that drains the battery. Is there an easy way to find this problem. In the past I usually disconnect the battery ground cable and remove one fuse at a time and look for a spark when reconnecting the cable which sometimes has led me to the problem. Are there other ways to diagnose this or could this be a bad relay as well? Thanks in advance Bill
Old 07-30-2007, 01:24 PM
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buy or borrow a cheap ammeter and start measuring current flow through each fuse. Any leak large enough to drain your battery overnight should be easy to measure.

Once you know which fuse the current runs through you'll be one step closer to the solution.

/ J
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Old 07-30-2007, 02:09 PM
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Check your relays too, specially the power window relay to see if it's hot to the touch after the key is out. A stuck window switch could drain your battery.
Old 07-30-2007, 02:28 PM
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Try like you've done before, except with a lightbulb in series where you'd look for the spark. The light will "spark" (glow) until you've disconnected all power draws.

Rob
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disconnect your negative battery cable, put your ammeter in series, then start pulling fuses to the draw goes away. An acceptable figure is usually under 25 ma. For a more accurate number, take the reserve capacity of the battery and divide it by 4.
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Depends How Fast the discharge is taking place. Certain items such as a clock or radio will slowly drain power for memory etc... If this is taking place over the season then they are the likely culprits. If it is taking place over a day or two, you may find that a glove box light, interior light or trunk light might be staying on. Before going through the fuse and relay thing, check the obvious and see if that is the problem. Have seen several trunk lights in other makes do this, it is not uncommon.
Old 07-30-2007, 04:52 PM
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The wires feel off my door switches inside the door jamb, which created an open circuit and drained my battery.
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Old 07-30-2007, 06:26 PM
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Quote:
Originally Posted by plymouthcolt View Post
The wires feel off my door switches inside the door jamb, which created an open circuit and drained my battery.

Old 07-31-2007, 01:20 AM
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Try like you've done before, except with a lightbulb in series where you'd look for the spark. The light will "spark" (glow) until you've disconnected all power draws.

Rob

i use to work for the best auto electric shop in charleston, the test light is the way to go. remove on e of the battery cables and connect one end of the light to the cable and the other to the battery, if it lights, you have a drain on the battery.
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Old 08-01-2007, 10:01 AM
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My door plungers corroded and WHEN my window switch failed it killed my battery!
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Old 08-01-2007, 10:54 AM
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I took Rob's advice and connected a 12 volt test light between the negative pole of the battery and cable and the light came on and actually flickered.. I unplugged all fuses and relays one a a time in the main relay board with no success. With the test light still connected and on. I then heard a ticking noise and took out the passenger seat and found this large relay or control unit ticking like a clock and unplugged the 2 multi-pin connectors and the light went out. I've posted a picture below. This appears to be the central locking relay part# 928 618 260 01. It appears that this is draining the battery The car would not crank with this relay unplugged. Can this one be repaired or bypassed? Any advice appreciated. Thanks BILL
Old 08-17-2007, 08:16 AM
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Sorry, I can't answer your answer regarding the central locking relay box you show.

However, I'd caution you not to use a test light on circuits that contain an electronic control unit (microprocessor). A 12V test lamp can draw excessive current through the nominal 5v feedback circuit and overload the electronics. Your '93 uses them for a multitude of comfort and convenience circuits. Current MY vehicles can have 10-20 ECUs throughout the elec. system, less so on older vehicles.

Better to use a multimeter which usually (the better ones) has high internal impedance so excess current isn't created when measuring circuit voltage.

Sherwood
Old 08-17-2007, 02:39 PM
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I don't know about that device, but keep in mind maybe it's supposed to run all the time so your keyless entry works all the time (like you'd expect a clock to run all the time). Like I said, I DON'T KNOW FOR SURE but don't be led too far astray by that without more info (I wouldn't personally spend hundreds of dollars on a new one without more concrete evidence it's bad).


Rob
Old 08-17-2007, 08:00 PM
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Bill, rereading your last reply I was reminded of my MINI wich had a battery drain problem over the last winter. It was fine through feb. but then dead in april, and actually died in a day's time once I got it out and started driving it. The stereo acted like it would scan for the cd over and over. Bad stereo right? I spent most of a day chasing every circuit in the car and couldn't stop the drain(s). Replaced the battery and all was well. Just something to consider.
Old 08-17-2007, 08:10 PM
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Taking Sherwood's advice I checked it again this time with a multimeter. With the control unit plugged in, I,m gettting a reading of 128m amps. With the yellow multipin plug disconnected from the control unit I'm getting around 30m amps. This car does have a factory alarm. The car will crank with the yellow plug disconnected from the control unit but I lose the central locking feature. Am I right in assuming that the control unit is the problem or do I need to do more investigating? Any advice appreciated. Bill
Old 08-18-2007, 07:28 AM
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Bill,
You may need a circuit diagram to fully diagnose the effect of this circuit on the ignition system. It's here on the site somewhere.

An ammeter is usually connected to a circuit in series so that all circuit current goes through the meter. Not sure how you connected it without a diagram of your hook up.

Sherwood
Old 08-18-2007, 10:46 AM
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battery drain

my clock was draining mine in about 1 week, removed the fuse and the battery did not drain down.. disconnected clock from the circuit for now.
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Old 08-18-2007, 07:56 PM
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