Are you hooking it up to a stock head unit? If it doesn't have a remote wire (usually blue) you can use switched power (usually red) off the head unit harness.
check out this website http://www.northursalia.com/modifications/misc/wiring/radiowrx.html BTW, james, which DD screen did you get?
on the back of the HU harness there's a 12v switched(red) a 12v always on(yellow). I dont like to run those as you might blow a fuse if you touch chassis ground. i prefer to use a tap splice on the ignition harness(blue plug by your key, i think it's the white wire with thin black stripe for ACC, go check though) for the remote wire, either that or you can get to it by jamming the wire in the fusebox in the correct slot(ghetto).