Well thats where the test light comes in handy. Find your fuse panel and probe some empty fuse slots or even ones with a fuse with the key on, if you find one that lights up the test light then turn the key off and see if it still lights it up. If it does light up with key on and off then you dont want that. That means it has full time power. If the light goes out when you turn the key off but lights up with the key on then your good to go. You can either splice into the wire behind that spot in the fuse panel or run your new wire into that slot in the fuse panel.