97 E320 Alarm won't turn off
 

Hello, I have a 1997 E320. Last week at night the alarm started randomly going off. I took out the battery to trickle charge it back to full strength but now whenever I reconnect the battery the alarm goes off and when I try to start the car the entire thing goes dead. I need to sell the car this week so I'm praying someone knows an easy fix to reset the alarm or how to disengage it. Thank you so much!