I have a 1987 300TD wagon. The battery was completely dead and autozone checked it out and said I needed a new one. Got the new battery and dropped it in. When I connected the negative after the positive the horn started honking. I then went and stuck the key in the door and moved it until it stopped honking. I tried to start it and got nothing. The wagon has been sitting for a little bit so I let the glow plug light come on and go off a few times before i tried to turn it over. I left it for about 3 hours and when I came back and tired to unlock the door the horn started honking again. I jumped in and put the key in the ignition to hopefully shut the horn off. When I put the key in the ignition it turned it all the way and got the motor to turn over really slowly. I probably got it to turn over three times and then i was back to just nothing. I could not get the horn to stop honking with out the key in the run position so I just un hooked the battery. I am a deffinate noob to mercedes and diesel cars and was hoping someone could give me some advice to get this thing runnin. I imagine it is something to do with the security system but I have no clue.