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Discussion Starter #1
My wife left her lights on last night and she woke me up to jump the car saying she was late for work. So here I go half asleep and I hook up the cables backwards.
The enging started cranking and the dash was all lit up. when I attached the cables the right way it turned over once and tried to start but stalled. Now the ignition circut seems out and it wont turn over. I found the alternator fuse blown and fixed it but no change. No other fuses are blown.

This must have happened before and Im sure the results are the same in most cases.
Can anyone tell me what to look for?
Thanks.
 

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2002 SLK 32 AMG, bone stock. 1987 190E 2.3-16 valve (destroyed). 2005 E320 new toy.
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14,926 Posts
I had a battery explosion in one of my other cars, it woke up half the neighborhood. He's right, you're lucky you didn't have one, the acid is a mess to clean up.

After you get a charge on the battery, turn on/check everything out and find out what doesn't work. Some electronics have circuits that protect them from reverse voltage.
 

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2002 SLK 230 1986 560SL 2008 Honda CRV
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3,664 Posts
You may want to invest in a surge protector for the battery which will save you from replaceing costly parts in the future. Do a search on anti zap or surge protector.
 

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98 Slk230
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231 Posts
Try tracing your wires to the starter or the starter solenoid/relay. Starter is probably fried.
 

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2003 SLK32 AMG
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101 Posts
I assume there was no "warning arc" when you connected the jumpers the wrong way around, otherwise this would have alerted you to the problem right away? If that is right, the battery must have been drawn completely flat, flat, flat. Most common automotive lead acid batteries don't take kindly to that and may not recover from it (plates buckle and so forth). Add to that the reverse connect.... Have the battery tested and unless its healthy start by replacing it. Maybe just your battery that's fried.

By the way, my SLK has a loud warning "beep-beep-beep..." if you take the key out the ignition while the lights are still on. This not the case with your wife's car?
 

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SLK
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probably just change the baterry.

Did you go from positive to negative and negative to positive or did you just have the black cable from the positive to positive and red cable from negative to negative? If the latter it wont matter. If positive on one car to negative on other your blown alternator fuse should be the only prob.

I had a battery explode in a C class years ago - located in the boot - what a mess.

A few years later I had one explode in an E class - located under the back right passenger seat. OMG what a huge mess!

MB batteries have a tendancy to explode. not fun
 

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SLK 320 BRABUS Modded
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We do it all the time on site, If a car had been untouched for a long time and the batt is total dead and will not take a charge, If you put it on charge the wrong way round for 30 secs then the right way 30% of the time it will hold a charge.

But not on the car lol :D
 

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Discussion Starter #11
Got her back today

Almost 4 weeks later and at a cost of $2700. She is all fixed. A few modules, fuses alternator and battery plus an oil change. I wonder what it would have cost at the stealership? probably 3 times that. Happy to have the top down again. :)
 

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2006 SLK 350
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Wow! That's an expensive situation. On the upside, it's an experience you'll likely not repeat (every time you prepare to do a "jump," this whole mess will replay in your mind).

I know the feeling of having my car back after a messy and costly mistake. Good luck to you.
 

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Got her back today

Almost 4 weeks later and at a cost of $2700. She is all fixed. A few modules, fuses alternator and battery plus an oil change. I wonder what it would have cost at the stealership? probably 3 times that. Happy to have the top down again. :)
Do you know what "modules" were burnt? Or does anyone know where I can begin to check for bad modules? I have done the same thing on my 98 slk 230 and have now replaced the battery, some various fuses including a red 40amp. Now the car still doesnt start and only cranks over 1 ot of ten tries. Every once in a while it will sputter when I turn the key but most tries I get complete silence minus what I believe is the fuel pump pressurizing the system.
 
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