Welcome to the Forum and the world of Vintage Airstreaming.
This may not apply to '68 models, but earlier in the '60s there were typically two switches that could be thrown resulting in problems that you describe. What I found with my '64 was that when an issue such as you describe arose either one or both of the following were true:
1.) If nothing other than the 12-volt circuits were working the master switch for shorepower/battery power selection was in the wrong position. In my Overlander it was in the streetside corner of the one-stop service compartment - - I am not sure where it would be found in a Caravel
or if it would have still been in use as late as '68. A good starting place would be to look between the shorepower entrance and the circuit breaker box.
2.) If the ceiling vent fans and range hood fan did not operate, the selector switch mounted on the wall near the kitchen window was in the wrong position - - on my coach this switch also controls the optional exterior electic outlet for the porchlight (the porch light was an option in addition to the typical "scare light" next to the entrance door). Again, this may not apply to the later '60s trailers but it is a possibility.
A third issue that applied to the earlier '60s trailers and may apply to your coach as well was that errant 12-volt problems were typically encountered if a battery wasn't present in the system.
Good luck in locating your electic gremlin.