Greetings William 8979!
As an addition to what Tom has already posted, I might add the following. Depending upon the extent of modification performed by previous owners on your 1955
coach, you will likely find at least some of the following to be true of your coach.
1.) Your coach would not have left the factory with a Univolt (or any power converter for that matter). Univolts did not become factory equipment until later in the 1960s - - if my notes are correct, 1964
was the first year that the Univolt was a standard feature.
2.) The coach actually had separate 12-volt DC and 120-volt AC light fixtures, and there may have been a separate umbilical cable just for these lights on your coach at one time (this extra cable is one feature that has often been changed-out by previous owners).
3.) The 12-volt side of the electrical system would have been powered by a 12-volt battery that was typically mounted in an aluminum box centered below the front window behind the LP tanks (it wasn't a typical Deep-Cycle battery as we know now), it was a farm implement starting battery that is still available through parts stores that carry farm implement batteries.
4.) There is a probability that you will find the 12-volt fuse panel behind the front lounge, and it may be hidden by an access door. On the later 1950s through the 1960-61 models that I have seen, the 12-volt fuse panel utilized what appear to be typical household screw-type "glass" fuses.
5.) There will likely be individual power transformers located near the furnace and the air pump for the water system - - these will usually be accompanied by a switch that must be thrown when power is switched from battery to shore power.
6.) If it hasn't been changed, your coach originally had a Bargman 120-Volt
AC power connection on the exterior of the coach that is almost impossible to replace in today's environment. If you have the original shore power cable and a working receptacle on the coach, it is something that needs to be handled carefully as the modern replacement will be much more obvious than the OEM Bargman assembly.
If your coach has escaped without significant changes, the refrigerator may be either strictly LP gas or possibly ice/120-Volt AC Electric. Again, this is a feature that often has been changed on a coach that is 40 or more years of age.
Good luck with your research!