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#1
07-25-2009, 04:37 PM
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Mercedes 400E 1991 battery Draining
I have a 1991 400E, and it has developed a problem with the battery being drained overnight.
It is sitting outside with a freshly charged battery. The battery is only a couple of months old, replaced when I put in a new alternator. I diconnected the negative cable, and I am measuring 4.25 amps draw with every single fuse pulled. I disconnected the alternator too, and the draw didn't change. There is nothing still on in the car... No lights, nothing. Where else can I look? I am a little stumped... The wiring diagram for this car is a nightmare... It's like 45 pages long or so... 
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#3
07-26-2009, 10:22 AM
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Not the radio...
I replaced the radio in this car back in 1996 with a Sony, and all the stock power amplifiers are gone. It has two Sony amps mounted under the rear deck (One for the speakers and one for the Subwoofer) along with a ten CD changer. (The sub is mounted under the cover for the original medical kit...)
Both amps are wired to the battery, the radio turns them on... But they are not pulling anything. I pulled the fuses first thing... No change. Then I started pulling fuses from the fuse box... I was surprised when the current draw didn't change with every single fuse in the car out... Then I thought it must be a bad alternator... I just replaced it a couple of months ago, but I thought that it could have a bad diode... When the draw didn't change with the alternator disconnected... That's when I was seriously confused at where the draw might be coming from... I figure it might be a relay somewhere that's on one of the "always hot" circuits... But damn, this car has a lot of circuits and relays! The wiring diagram is kind of an unholy mess... i am not even sure how many pages it is, but it's somewhere between 45 and 60 pages... Thanks for any help anyone can give me on this...
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#4
07-26-2009, 11:50 AM
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pull the fuses one by one until the drain goes away. One you have isolated the circuit then start looking at all possible consumers on that circuit. do the ampdraw test all doors closed, key out and must be done in series.
__________________
1986 300SDL, 211K,Dealership serviced its whole life 1991 190E 2.6(120k) 1983 300D(300k) 1977 300D(211k)
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#6
07-26-2009, 08:22 PM
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do you have an immbolizer installed?
next suggestions is to look at the power distribution wiring diagrams and see whats hot all the time. Download 1030 - Testing no-load current consumption Model 124.pdf from FileFactory.com
__________________
1986 300SDL, 211K,Dealership serviced its whole life 1991 190E 2.6(120k) 1983 300D(300k) 1977 300D(211k)
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#7
07-26-2009, 11:46 PM
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You can get a really good infrared thermometer for about $50-60 online.
Could the problem be the starter solenoid? Starter switch? Seems like those are some of the only things still connected.
__________________
-diesel is not just a fuel, its a way of life-  '15 GLK250 Bluetec 118k - mine - (OC-123,800) '17 Metris(VITO!) - 37k - wifes (OC-41k) '09 Sprinter 3500 Winnebago View - 62k (OC - 67k) '13 ML350 Bluetec - 95k - dad's (OC-98k) '01 SL500 - 103k(km) - dad's (OC-110,000km) '16 E400 4matic Sedan - 148k - Brothers (OC-155k)
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