I'll assume that your latch mechanism is similar to the ones on my cars. If you examine the part that the keylock/button pushes on to release the part of the latch on the trunklid, it should be possible to drill a small hole in it and attach a short cable. From there, just get any trunklatch solenoid from the junkyard and mount it to pull the cable when 12V is applied. Get the button from the same car and mount it inside. I've not done this on a Mercedes, but I did set up a remote latch on my streetrod trunklid this way.

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1986 560SL
2002 Toyota Camry
1993 Lexus