electrical problems - new battery drains overnight

Bigbartguy · 04-02-2002, 09:09 PM

electrical probs - new battery drains overnight, help needed:

1. installed new battery, went out 2 days later and it's dead already. car had only been started once since the new battery was installed, for about 5 minutes.

2. disconnected and recharged battery. Checked battery voltage: 13.96

3. placed VOM between positive cable and battery. 13.96 still, so something is draining all of the batteries available power.

4. began pulling fuses. reading remained at 13.96 after each fuse had been pulled.

5. began pulling relays (here's where it gets a little foggy, as I'm not exactly sure how many relays there are) - pulled 2 from engine comparment, pulled 2 more similar ones from luggage compartment (way back near the firewall), and pulled all of the round relays above the fuse box. reading remained at 13.96. IS THIS ALL OF THEM?

my conclusion is that something not connected to a fuse/relay is draining my battery while parked. If I had found the fault, the voltage drain would have dropped.

6. what could this be? the car came with an aftermarket cd changer in the trunk, could this be the problem?

7. alternator or diode or regulator? any way that I can test which?

8. I'm pretty clueless when it comes to electrical issues, any advice would be GREATLY appreciated.

thank you
Tim

Early_S_Man · 04-02-2002, 09:28 PM

Tim,

If there is a shorted rectifier diode in both the positive and negative arrays ... it will drain a battery overnight, or even in a few hours, sometimes!

To test the arrays, they must be unsoldered from the stator windings. There are three diodes in each array. The third 'exciter' array is not part of this scenario!

Once removed ... the rectifier arrays may be tested with a multimeter, or taken to an alternator/motor repair shop for testing.

Wayne 962 · Wayne 962's Garage

Eliminate the battery - run an ammeter between the battery and the car and check for actual current. Voltmeter won't tell you much. You might not see a voltage drop with a very small drain...

-Wayne

911pcars · 04-03-2002, 01:07 PM

Wayne's right. You should connect an ammeter between the positive battery post and the pos. cable, then start removing fuses and harness connectors (for those circuits not fused) while monitoring current level to isolate the offending circuit. A wiring diagram will come in handy too since many circuits share a common fuse.

Sherwood Lee
http://members.rennlist.org/911pcars
www.seinesystems.com

sammyg2 · 04-03-2002, 06:23 PM

I had a similar problem when I bought my car, but it would drain down in about 4 days instead of overnight.
I isolated the drain to the positive wire that goes to the starter and alternator. Then I traced it back farther and found the starter was not the drain, that left only the alternator. I pulled it and had it rebuilt, no more problems :-)

Bigbartguy · 04-03-2002, 07:11 PM

I finally thought enough to try pulling the 2 'add-on' leads off of the positive lead connected to the battery.

There are 2 extra 'leads' that connect to the positive battery post in addition to the BIG lead.

1 lead has 2 or 3 red wires running into a connector that attached to the post - it's fine.

The other lead is a single wire, encased in black 'tape'. It is actually a red wire though. Checking this lead dropped my voltage to almost nothing. This appears to be the problem, although it runs back into the array of wires under the fuse box and I have no idea to find out what this wire controls and am unable to manually trace the wire.

Does anyone know what this lead is or can suggest a way to find out ? Is this the wire that goes back to the starter and alternator? I REALLY appreciate this advice.
thanks again
Tim

pwd72s · 04-03-2002, 07:27 PM

Silly question...is your interior light on?

Bigbartguy · 04-04-2002, 04:11 AM

NO, but I wish !!!
the interior light works and isnt on.
Tim

Roland Kunz · 04-04-2002, 11:03 PM

Hello

Silly question...is your trunk light on?

bluskyflier · 04:19 AM

The same things was happening to my 1995 911/993. The culprit was a light bulb that illuminates the display at the bottom center of your tachometer that toggles the computer to share outside temp, speed, range, etc. It is very hard to notice specially when you exit the car and the light is not bright and appears to be off or the top is down and it is sunny (usually the case).

Best of success and hope that helps.

Oh Haha · 05-09-2010, 04:22 AM

Had the same problem recently.

You really can only trace the wire to the end to find out what it powers. It does sound like it was added by a PO.

Do you have an amp or any other powered components?

My problem was the wiring on the headlight switch was incorrect(my own mistake, btw).

Good luck with finding the problem. Please post back what you find.

docrodg · 05-09-2010, 05:36 AM

Measuring voltage will not tell you anything in this case. You need to measure amps. Voltage is POTENTIAL difference between two points (think of a tank full of water on a tower with a pipe going down with a valve on the end, there is pressure at the pipe on the bottom whether the valve is open or not. Amps would be akin to the flow of that water. Disconnect the positive battery cable and measure the amp drain and write it down. Then you can find the circuits with a drain by reconnecting the battery and measuring the amps at the fuse block for each circuit. Always disconnect the circuit you are measuring and insert the ammeter into it, do not just probe two points.

Oh Haha · 05-09-2010, 05:41 AM

Here is the link to my thread. I was given some great guidance by those with more knowledge than I.

battery drain----searched already

scottbombedout · 05-09-2010, 06:04 AM

Quote:

Originally Posted by bluskyflier

The same things was happening to my 1995 911/993. The culprit was a light bulb that illuminates the display at the bottom center of your tachometer that toggles the computer to share outside temp, speed, range, etc. It is very hard to notice specially when you exit the car and the light is not bright and appears to be off or the top is down and it is sunny (usually the case).

Best of success and hope that helps.

The original thread was 8 years ago. I hope he got it sorted!

Oh Haha · 05-09-2010, 06:56 AM

Well, THAT'S embarrassing.

86 911 Targa · 07:40 AM

Quote:

Originally Posted by Bigbartguy

I finally thought enough to try pulling the 2 'add-on' leads off of the positive lead connected to the battery.

There are 2 extra 'leads' that connect to the positive battery post in addition to the BIG lead.

1 lead has 2 or 3 red wires running into a connector that attached to the post - it's fine.

The other lead is a single wire, encased in black 'tape'. It is actually a red wire though. Checking this lead dropped my voltage to almost nothing. This appears to be the problem, although it runs back into the array of wires under the fuse box and I have no idea to find out what this wire controls and am unable to manually trace the wire.

Does anyone know what this lead is or can suggest a way to find out ? Is this the wire that goes back to the starter and alternator? I REALLY appreciate this advice.
thanks again
Tim

Tim,

Now that you have fault isolated the parasitic current draw, you need to do a leak test with your multimeter to determine the magnitude of the current draw.

"Assuming" that you have an 80+ Amp battery, your current drain appears to be >1 Amp/Hr.

Another idea is, while your meter is measuring the current draw as per the attached jpeg, pull the fuses one at a time.

If you find the defective circuit, check the fuse/relay cover for circuit I.D., and lift the wires at the fuse output.

This should I.D. the deffective wire/circuit.

You may pm me.

Good luck,

Gerry