what does a bcm module control do

Question

my instrument cluster lights up for to crank only thing I have no crank and no instrument cluster light I also can hear all my relay clicking for about 30 seconds I previously put the wrong bcm but then tried to put my old 1 back in what are the key was in the on position not realizing it was on I replaced and reprogram my pcm what could be the problem the vehicle will start with a scan tool hooked up to it but it will not start on its own could it be a blown bcm

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