Have u pulled the fuse out and checked the connection that the fuse goes into? See if there is power there, could be a bad connection onto the fuse. But if not there should be no reason there is no 12+ live there because it is a permanent live, it's not switched through any relays or ignition switch. it will be straight of the battery bus bar in the back of the fuse box. Which fuse box is the fuse in?
Have u done anything to the car at all? New stereo? Even though I'm a auto sparky not done much work on mine yet. I'll look on diagram mate 2mins but pretty sure it will just link of bus bar like all other fuses. I've not got my liner here so can't look but is there other permanent fuses in that fuse box? Like hazard lights? Central locking? Radio permanent live? Cig lighter? Is the hole fuse box missing a live? Or does all that work? There might even come of a diffent fuse box