Power center problem

Are you reading the voltage across the fuse terminals (or where the fuse would go)? If so, having a very high resistance on the load side, nearly an open circuit, would make your meter show something other than 12V. Having an entirely open circuit would result in basically no reading as there's no path to ground. Slightly more useful is to check the voltage from the source side of the fuse to a known ground point; they should all be at (nominal) +12V and all be the same. Since a meter doesn't provide any significant load, though, it doesn't tell you much beyond there's some connection there; in particular, it tells nothing about how good that connection is.