I HIGHLY suggest you get a qualified electrician in to look at what you have. Yes, it will cost you, BUT it will save you from miswiring the plug and causing bad things to happen.
I'll also say this. Typically, a camper that old is going to need some work done on it, will you be doing the work or do you have someone else lined up to do it? If you aren't very experienced in handyman type fixes, you might have bought yourself and expensive project.
2011 F150 Ecoboost SCREW 145" 4x4
Firestone Ride-Rite Air Springs/Air Lift Wireless Controller
2006 Sportsmen by KZ 2604P (30')
X2 on that. Wiring from the 1950s is almost certainly not going to have a third grounding wire, or items that are essential safety items. I'd get an electrician with RV knowledge to rewire it up properly, so you have a ground and no chance of the outer skin of the trailer ending up energized.
I mentioned this on a previous post, but it also can't hurt to have a switch rated circuit breaker located nearby where the cord comes in. This way, you can flip the circuit breaker off, plug/unplug your cord, flip it back on and not worry about arcing.
If you check the plug and it is indeed a 15amp look closely at the plug and notice that the one prong on the male plug is larger than the other one. Then if you are going to attempt putting a new plug on yourself look carefully at the plug and see if one of the prongs is also larger than the other! When you take the old wires off the old plug make sure you check to see which wires come off the larger side of the plug so you can put them on the larger side of the new plug or you will have your RV wiring reversed, AND THAT IS NOT GOOD. Good Luck Gary.
* This post was
edited 04/13/12 04:15pm by Gary. *