I'm not sure what where to connect the system control (blue) wire to my DEH-P690UB Pioneer deck?

I have a 2001 mercury sable ls and i ran all the wires from the deck to the amp which is in the trunk of my car; the system control wire, rca cables and the remote cable and everything. Everything except the system control wire is connected to the deck, every things set up on the amp. All i need to do is hook up the system control wire to the deck, but i don't know where it's supposed to go on the back of the deck. Also i don't have the power cable hooked up to the battery. I know it's gotta go through the firewall or something; one, i don't even know where that's located; and two, do i need to drill a hole?