Mercedes ignition problem HELP

I have a very weird case. I turn off my key and
when I pull it out the ignition doesnt lock, in order
for the ignition to lock I have to pull the switch for  
my lights (activating my brights) then I here the
ignition lock. Then I'll get out lock my car and
within 3 to sometimes up to 30 min the dash will
light up and radio will one on as if some one
inserted a key and turned it to positionn 1. This is a  
HUGE PROBLEM because not only does it drain the
battery but I have a breathalyser interlock system
and this machine then also thinks I someone put a
key in and that's a violation for the machine if no
blew. Which then activates the breathalyser bulk in
alarm the wakes everyone up or goes off in parking
lots . PLEASE HELP !