50 amp service is 4 wires. 2 hot leads (black) and one neutral (white) one ground (green or brown)
By junction box, do you mean the automatic transfer switch? That box has 3 large (50 amp) cords connected. One is the shore cord, one from the generator, and one connecting to your main breaker panel. All are 4 wire lines.
In an RV that doesn't have an automatic transfer switch, the power from the generator usually ends in a 30 or 50 amp outlet. The shore cord is wired directly to the breaker box. To use the generator, the shore cord is plugged into the generator outlet.
The generator should have 2 circuit breakers on it's panel, be sure to turn them off then on again to reset them.
In some RVs, the shore cord is 30 amps. It isn't enough power to run 2 air conditioners. The generator is 50 amps, and it can run both A/C. One A/C is wired to the 30 amp shore cord, the other is wired to the generator on the other 'leg' of 50 amp power that is not wired through the breaker panel.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI