The power problem your speaking of can be any off the three things that you listed. Mine was the wiring loosing it's sheilding and the ground cable rotting away. Luckily it was covered under warrenty.
As far as the Timing belt it's a good idea to replace it around 60K when the manual says. You can check it to see if there are cracks like the Serpentine belt but hte tell tail slapping on start up (Pre 98) will let you know.
