which model and year?

I have a 2000 Mercedes benz s430 and the battery is dead so i can't unlock the trunk remotely or with the mechanical key. can anybody help me....thanks

Can you open the drivers door with your key ( to unlatch the hood )?

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2007 C 230 Sport.

one door was left open and i can't unlock or lock the doors remotely. cannot unlock the trunk using the switch on the door too.

There is a positive terminal under the hood, you can jump power using jumper cables to that terminal, then the power locks will work. I think that's what Manny is getting at.
The mechanical key WILL open the trunk. You put the key in and rotate it (either clockwise or counter clockwise, forget which) then push IN on the key/lock cylinder. This is all in the owners manual.
Gilly

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i tried using the mechnical key and the instruction manual, still won't unlock. There is no positive terminal under the hood and the manual doesn't mention or show it either. thanks

is there a positive connection to the alternator?