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2005 SL500 2005 S500 2018 GLC 300 coupe
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Discussion Starter #1
I have recently purchased a 2005 SL500 that had been seating in unheated storage since 2010 with the top down. I didn’t even try to save the batteries I just replaced them with new ones from the dealer. After clearing a large amount of codes from seating so long, I’m down to just two that seem to have nothing to do with my current problem. An Ac cycling switch and a Vario roll bar positioning fault. After the car sits for a couple of hours the battery totally disconnects from the car and shut everything down and makes it forget what in its memory and makes it unable to unlock the doors or open the trunk. But as soon as I place the key into the ignition and turn it twice everything jumps to life and the car will start, but it acts like the batteries behave been disconnected and then reconnected it has no memory of what was stored. I have replaced the starter fuse and the relay in the trunk and placed a drawn down tester and still have no idea where to go from here. No red warning lights on the dash and no new codes that would lead me to believe anything more then a lose of power after it sits. Any help or direction would be greatly appreciated
 

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2003 SL500, 2003 SL55, and four R129s
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4,366 Posts
It seems as if your rear battery isn't even connected to the electrical system, though this is implausible.

I think you are simply going to have to check power distribution throughout the vehicle with a voltmeter. I've attached a diagram of the electrical system to provide an overview. Likely you'll need more detail to make voltage measurements, and for that you can download all of your vehicle's wiring diagrams here: R230 ETM 64. Double-click on the msi file to install the diagrams along with the parts locator program Starfinder.

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R230 Power Diagram.png
 

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Registered
2005 SL500 2005 S500 2018 GLC 300 coupe
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6 Posts
Discussion Starter #3
Thanks for the info. I was thinking some wiring diagrams would need to be my next step. But All-data wasn’t being much help with the right diagrams.
 

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Outstanding Contributor
2003 SL500, 2003 SL55, and four R129s
Joined
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4,366 Posts
Incidentally, if you right-click on a diagram you can choose to change the behaviour of the mouse cursor to either pan all around or zoom in and out.
 
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