Like Russ stated, it depends on where you checked for power. It could be several things.. The ignition switch for one, the older ones some times arc and quit, the next time you turn it it may knock off the arc spot. I have been working on my 69 and I had ignition switch on for a couple of hours and it killed the coil. The fuse box can also be doing the same thing. They get rusty and don't always make good contact. Granted they are in a very hard to get at place to clean. One of the members used ketchup (acid in the tomatoes) to clean his dimmer switch, this may be a good thing to tune up the fuse box. Good Luck