Alarm on my S420 goes off how do i stop
 

On my 1995 s420 I replaced my dead battery with a new one. Installation was fine but the alarm goes off and I can not turn it off without disconnecting the battery. Owners manual does not help. Any help will be appreciated.

the square key inserted into the driver's door and unlock the door should shut off the alarm.
if you wish to disable it, 124's have a panel under the front passenger's floormat. the alarm computer is in there, not sure if the 140's are the same...

Is that a 1995 S420 W140 chassis OR is it a 2000 or later S430 W220 chassis??

1995 is the 140 chassis.

Using a key in either front door OR in the deck lid should cancel the alarm.

Using the remote should always cancel the alarm.

If not, most likelt the control unit is bad. Disconnect it