2004 Blazer: want to trigger rear defrost

My Autocommand remote starter has a (-) pulse output that I would like to use to trigger my 2004 Blazer's electric defroster grid timer switch. I am not sure if  (or where) I can connect into (the BCM or defroster switch) to do this. I haven't found a good wiring chart or schematic that helps either.

Any ideas? It sure would be nice to have the mirrors and rear window clear while the truck warms up!

Chuck,

dont know if this will help, but if you can find the relay that works your heater, you are half way there. Connect the (-) wire from your starter to the side of the relay that comes from the heater switch.

Sorry cant be more specific, but in UK, dont have blazers !!!!!

Dave.

Thanks. I have asked guys on another site where the elusive relay may be hiding. Hopefully somebody here (or there) will chime in with that info.