Why won't the alarm stop?

[Jdukey]

Hi,

I have finally got around to starting work to bring my Grandad's w203 C180 back on the road. I believe I have everything I need. However, it has sat for nearly a year without being run, so as you can imagine the battery is totally flat (won't even remove the ignition lock). I have got a spare charged battery and a set of leads and I have been able to start the engine using this method, but as soon as I connect the leads the alarm goes off. And it keeps going whatever I do with the key/ignition. Does anyone know if there some kind of procedure for doing this to avoid the alarm going off?

Thanks
James

Edit:

The same happens if the old battery is removed and a new one fitted. The boot also will not open either with the button inside or the button on the remote (but will with the manual overide). Neither will the car lock or unlock via the remote.

 

[BlackC55]

The siren battery is kaput

 

[Jdukey]

Yeah, that would make sense. In that case, is there a way I can disconnect the siren for now? That way I can attempt to fix the other (slightly more fundemental) problems in peace and deal with a replacement battery later.

James

 

[Jdukey]

Having left the engine running for a significant period of time, this problem seems to have evaporated. Maybe the backup battery has been recharged?
Thanks for the help anyway.

James