I have recently purchased one of those scanning light things for alarms and such, like the one here

http://cgi.ebay.com/ebaymotors/ANTI-...95956787QQrdZ1

I was wondering, what wires on the truck are hot when it is turned off, and cold when it is on, so that my alarm light will come on when I turn the truck off. If I had an aftermarket alarm, I would just hook it up to that light, but I dont. Any Help would be great,
thanks