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  #1  
Old 09-14-2006, 02:02 AM
sixto's Avatar
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93 300SD electrical drain

[moderator, this thread is cross-posted in tech help]

I drove the SD on Monday and everything was fine. I tried to start it on Wednesday and the battery was flat. No remote keyless entry, no dome lights, nothing. I hooked up a fresh battery but before hooking up the ground cable I checked current draw - 3.25 amps! I pulled all the fuses in the engine bay fuse box, trunk fuse box and disconnected the glow relay - still 3.25 amps. I'm thinking of tracing the power cable, then pulling each of the ECUs. Does anyone have guidance on how to proceed?

Thanks,
Sixto
93 300SD

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  #2  
Old 09-14-2006, 02:06 AM
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Disconnect the power wire from the alternator. Check the ammeter.
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  #3  
Old 09-14-2006, 03:24 PM
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I disconnected the big and small wires at the alternator and starter, and the small wires near the battery. The only thing I can't trace is the big cable from the battery to wherever it goes. Still 3.25 amp draw.

alldatadiy doesn't have a diagram that shows distribution or routing of the big cable.

Other thoughts?

Thanks,
Sixto
93 300SD
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  #4  
Old 09-14-2006, 03:47 PM
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I experience the same battery drain, although I haven't measured how much. If I don't drive everyday, I can't start . I have a small charger that I would let it charge over night every week or so. Mine is a 1992.
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Last edited by Californian; 09-14-2006 at 04:40 PM.
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  #5  
Old 09-14-2006, 03:54 PM
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Quote:
Originally Posted by sixto View Post
I disconnected the big and small wires at the alternator and starter, and the small wires near the battery. The only thing I can't trace is the big cable from the battery to wherever it goes. Still 3.25 amp draw.
That's a lot of current to simply be disappearing. And, if it's not fused through the box, what's protecting it??

Seems really strange.............
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  #6  
Old 09-14-2006, 04:09 PM
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Test

Verify all accesories are off. Remove fuses one a time and carefully. Recommend using 10 amp fused jumper wire in series (in line) with test light connect test light across terminals. Start with power always on circuits, E.G. courtesy lights, trunk light ect.
If test light comes on that is trouble circuit. Isolate problem in circuit with wiring diagram.
Make sure before starting that all acc.s are off. Remove key from ign. Do visual on all lights.
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  #7  
Old 09-14-2006, 05:44 PM
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The set-up as I see it is battery in trunk, ground to frame, 2 (+) cables - a small one to a distribution block, one big disappears into the rear firewall.

I removed:

- all the fuses, not one at a time, all of out at the same time

- both alternator wires

- both starter wires

- all glow relay connectors

- all ECUs in the engine comparment

- the smaller cable into the juction block by the battery

Still 3.25 amp drain.

What I'd like to see is a wiring diagram showing the path of the big cable and what it connects to.

Could there be an SRS capacitor that is charging at 3.25 amps because I keep connecting and disconnecting the battery? That won't explain why the battery went flat sitting for 2 days.

Thanks,
Sixto
93 300SD
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  #8  
Old 10-17-2006, 05:04 AM
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Quote:
Originally Posted by Californian View Post
I experience the same battery drain, although I haven't measured how much. If I don't drive everyday, I can't start . I have a small charger that I would let it charge over night every week or so. Mine is a 1992.
I have the same problem.What is the name of the charger you use?I want buy it.How long can I leave my car without the battery problem?

Thanks
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  #9  
Old 10-17-2006, 01:22 PM
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Location: ohio
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I had same problem and it turned out to be the amplifier (for the speaker system) located in the trunk staying on. You could feel its warmth for hours after everything was shut off. Pull the power wire from the rear radio configuration to the amplifier. That will stop any drain. It is also common for the power antenna motor to stay on. To check that simply pull the power wire going to antenna motor. Pulling fuses wont help in these 2 issues.
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  #10  
Old 10-17-2006, 01:36 PM
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Quote:
Originally Posted by sixto View Post
Could there be an SRS capacitor that is charging at 3.25 amps because I keep connecting and disconnecting the battery?
A capacitor will draw a lot of current for a short time (~seconds) and then stop. However, if the capacitor developed a short-circuit, it would draw current forever. If so, it would get warm and you could feel it if you can get at it.

This is a fascinating problem and I am looking forward to reading the answer in the back of the book.

Jeremy
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  #11  
Old 10-17-2006, 05:47 PM
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Antenna motor is disconnected. Could be the amp.

There's another post about the AC blower continuing to run with the key out.

Sixto
93 300SD
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  #12  
Old 10-17-2006, 11:41 PM
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Rest function?

Sixto,

The 140 has a "rest" button on the ac controller. This is to keep cabin temps up to the selected setting while the car is not running. It -> should <- stop when the battery level reaches a lower level or the coolant temp is below a defined level. That could keep your fan running a while, but it should shut off in less than an hour.

Chuck

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