On the alarm there should be a place for the led light to plug into. If not you should be able to find a relay at radio shack, you will have to ask there to get the right one, what you will have to do is use a power on wire when key is on wire that to energize the relay which will kill power to one of the other terminals and when you turn the key off the relay will switch to another pole and wire a constant power wire to that.
Danial Dickinson "You can bone us; but you don't own us" RESCUE AIRCRAFT MAINT.